Programmable gate array with improved interconnect structure, input/output structure and configurable logic block

ABSTRACT

A programmable gate array with an improved interconnect structure facilitates multi-source networks, communication of signals long distances across the array, and creation of networks in a symmetrical interconnect structure. The interconnect includes direct connections for each configurable logic block in the array to eight neighbors, including adjacent configurable logic blocks and next adjacent configurable logic blocks. Also, the interconnect includes uncommitted long lines which are driven by outputs of configurable logic blocks but not committed through the interconnect to inputs of any specific logic block. Rather, the uncommitted long lines are committed to connections to other segments of the interconnect. The interconnect structure also includes staggered switching matrices at the intersections of the horizontal and vertical buses in the interconnect. Repowering buffers that are configurable in both directions are associated with bidirectional lines in the interconnect, and include a bypass path. The interconnect provides for communication of control signals from off the chip, from any configurable logic block in the array, and from the input/output structures in the array to any or all other configurable logic blocks and input/output blocks in the array.

This application is a divisional of copending Ser. No. 07/394,221, filedAug. 15, 1989, and issued as U.S. Pat. No. 5,212,652.

FIELD OF THE INVENTION

The present invention relates generally to programmable logic devicesand, more particularly, to programmable gate arrays consisting of anarray of logic blocks and input/output blocks with an interconnectionstructure, each of which are configurable by a configuration programstored in on chip memory.

DESCRIPTION OF RELATED ART

The programmable gate array is a high performance, user programmabledevice containing three types of configurable elements that arecustomized to a user system design. The three elements are (1) an arrayof configurable logic blocks (CLBs), (2) with input/output blocks (IOBs)around a perimeter, all linked by (3) a flexible programmableinterconnect network.

The system design desired by a user is implemented in the device byconfiguring programmable RAM cells. These RAM cells control the logicfunctionality performed by the CLBs, IOBs and the interconnect. Theconfiguration is implemented using PGA design software tools.

It is generally accepted that the programmable gate array was firstcommercially introduced by Xilinx of San Jose, Calif. Xilinx originallyintroduced the XC2000 series of logic cell arrays and has more recentlyintroduced a second generation XC3000 family of integrated circuitprogrammable gate arrays. A description of the 2000 series, as well asrelated programmable logic device art, can be found in THE PROGRAMMABLEGATE ARRAY DESIGN HANDBOOK, First Edition, published by Xilinx, pages1--1 through 1-31. The architecture for the XC3000 family is provided ina technical data handbook published by Xilinx entitled XC3000 LOGIC CELLARRAY FAMILY, pages 1-31. Each of these Xilinx publications isincorporated by reference in this application as providing a descriptionof the prior art.

The prior art in programmable gate arrays is further exemplified by U.S.Pat. Nos. 4,642,487; 4,706,216; 4,713,557; and 4,758,985; each of whichis assigned to Xilinx, Inc. These U.S. Patents are incorporated byreference as setting forth detailed descriptions of the programmablegate array architecture and implementations of the same.

As mentioned above, the programmable gate array consists of aconfigurable interconnect, a ring of configurable input/output blocks,and an array of configurable logic blocks. It is the combination ofthese three major features that provides flexibility and data processingpower for programmable gate arrays. However, the programmable gatearrays of the prior art suffer certain limitations in each of theinterconnect structure, the input/output block structures, and theconfigurable logic block structures.

The configurable interconnect structure must provide the ability to formnetworks on the programmable gate array which optimize utilization ofthe resources on the chip. The prior art interconnect systems havetended to force connection in the logical network to configurable blocksin a relatively small area. For instance, a prior system provides directconnections only between adjacent configurable logic blocks. The inputsand outputs on the configurable logic blocks are arranged in a left toright or otherwise asymmetrical layout that forces signal flow in acertain direction across the chip. This causes congestion on theinterconnect structure for applications requiring a large number ofinputs or outputs. Also, this forces the printed circuit board layout,which includes one of these asymmetrically designed logic cell arrays,to provide for inputs on one side of the logic cell array and outputs onthe other.

In addition, the prior art interconnect structures are limited in thenumber of multi-source networks that can be implemented.

The input/output blocks in the prior art programmable gate arrays arerelatively complex macro cells in order to provide flexibility neededfor the wide variety of applications intended for the devices. However,these complex macro cells include resources that are unused in manyconfigurations of the input/output blocks. Further, the blocks arerelatively slow because of the complexity, requiring passage through anumber of buffers, multiplexers and registers between the logic cellsand the input/output pad. Furthermore, the input/output blocks causecongestion on the peripheral logic blocks in the device for applicationsinvolving a lot of input and output.

The configurable logic blocks themselves also suffer limitations whichimpact the flexibility of the device. The logic blocks of the prior arthave operated upon a relatively small set of input variables. Thus, widegating functions, such as decoding a 16 bit instruction or a widemultiplexing function, required cascading of many configurable blocks.Thus, a very simple function can utilize a large number of configurablelogic blocks in the array. Further, when cascading blocks, due to thelimitation of the number of direct interconnections between the logicblocks, many of the signals have to be transmitted across theprogrammable general connect. This causes delay because of the number ofprogrammable interconnection points used. Further, for critical pathsrequiring fast operation, the cascading of blocks becomes impractical.

In the prior art configurable logic blocks, typically four input signalsare used for the logic function. In order to obtain a five variablegating function, the configurable logic blocks used a sharing of inputsscheme. This sharing of inputs greatly limits the logic flexibility forthese five variable functions in the prior art.

Prior art configurable logic blocks also suffered speed penaltiesbecause of the relatively complex structure required for the blocks toachieve user flexibility. For a block which is being used for a simplefunction, the logic would be propagated at a relatively slow ratebecause of the complex structures required.

It is desirable to provide a programmable gate array which provides forgreater flexibility and logic power than provided by prior art devices.

SUMMARY OF THE INVENTION

The present invention provides an architecture for a configurable logicarray with an interconnect structure which improves flexibility increating networks to allow for greater utilization of the configurablelogic blocks and input/output blocks on the device.

Accordingly, the present invention is an improved configurable logicarray comprising a configuration memory storing program data specifyinga user defined data processing function. In addition, a plurality ofconfigurable logic blocks are arranged in an array consisting of Ccolumns and R rows. Each configurable logic block is coupled to theconfiguration memory and has a plurality of inputs and outputs forgenerating output signals at the respective outputs in response to theinput signals at the respective inputs and in response to program datain the configuration store. A plurality of configurable input/outputblocks is included, each coupled to an input/output pad and to theconfiguration store, and having at least one input and at least oneoutput. The configurable input/output blocks provide configurableinterfaces between the respective pads and the respective inputs andoutputs in response to the program data. A configurable interconnect iscoupled to the configurable logic blocks, configurable input/outputblocks and to the configuration store, for connecting the inputs andoutputs of configurable logic blocks and configurable input/outputblocks into logical networks in response to the program data in theconfiguration store.

According to one aspect of the invention, the configurable interconnectis symmetrically disposed relative to the inputs and outputs of theconfigurable logic blocks. Thus, inputs of the CLBs can be derived fromfour sides and outputs can be driven to four sides of the respective CLBinto a symmetrical interconnect structure.

The interconnect includes a plurality of horizontal buses along the rowsof CLBs and a plurality of vertical buses along the columns of CLBs. Theintersections of the horizontal and vertical buses are configurable toroute networks across the device.

Another aspect of the interconnect includes a plurality of switchingmatrices at the intersections of horizontal and vertical buses, eachhaving a set of horizontal connections and a set of verticalconnections, for interconnecting respective ones of the horizontal orvertical connections in response to program data in the configurationstore. A plurality of horizontal conductive segments in the horizontalbus are connected between the horizontal connections of the switchingmatrices. A plurality of programmable interconnect points coupled torespective inputs and outputs of the configurable logic blocks andinput/output blocks provide connectability to respective horizontalsegments in response to program data. Likewise, a plurality of verticalconductive segments in the vertical bus are connected between thevertical connections of the adjacent switching matrices. Programmableinterconnect points interconnect the respective inputs and outputs ofconfigurable logic blocks and input/output blocks with respectivevertical segments in response to the program data. The vertical andhorizontal segments, according to one aspect of the invention, arecharacterized by extending from a switching matrix in a vertical orhorizontal bus "i" to switch matrix in bus "i+2", so that each segmentspans two columns or rows of logic blocks.

The buses in the interconnect are further characterized by a pluralityof horizontal and vertical long conductive lines which extend across theentire chip. Each long line is connected to a plurality of programmableinterconnect points for interconnecting the respective inputs or outputsof configurable logic cells with the respective long line in response toprogram data in the configuration memory. The long lines arecharacterized by having programmable interconnect points coupling anoutput of a configurable logic block which is supplied by a tristatebuffer to the respective long lines.

In another aspect, the buses in the interconnect structure arecharacterized by uncommitted horizontal and vertical long lines. Eachuncommitted long line is connected to a first plurality of programmableinterconnect points for interconnecting the respective outputs ofconfigurable logic blocks or input/output blocks with the respectivelong line in response to program data, and a second plurality ofprogrammable interconnect points for interconnecting respectiveuncommitted long line with the horizontal or vertical segments that arecoupled to the switching matrices.

The interconnect structure further includes a plurality of directconnections interconnecting an output of a configurable logic block orinput/output block to an input of another configurable logic block orinput/output block. The direct connections are characterized byincluding at least a first subset which are connected between adjacentinput/output blocks or configurable logic blocks, and a second subsetwhich are connected between the output of a configurable logic block orinput/output block and a next adjacent configurable logic block orinput/output block. In one aspect of the invention, each CLB is directlyconnected to 8 neighbor CLBs.

The plurality of configurable input/output blocks is characterized bygroups of input/output blocks associated with each row or column ofconfigurable logic blocks. Within each group, at least one complexinput/output block is included and at least one simple input/outputblock. The complex input/output blocks provide the flexiblefunctionality required for many applications, while the simpleinput/output block provides a fast access path into or out of theconfigurable array.

Further, all of the input/output logic blocks are characterized bytristatable output buffers to pads and to the internal interconnectwhich are controlled in response to the program data and/or a controlsignal generated in the configurable logic array.

Also, the outputs of the configurable logic blocks include a pluralityof tristate buffers which receive respective ones of the output signalsof the combinational logic and tristate control signals. The tristateoutput buffers supply a respective output signals or present a highimpedance state as output from the logic block in response to thetristate control signal. The tristate control signal is generated inresponse to the program data in the configuration store and an input tothe configurable logic block.

Another aspect of the invention is configurable repowering buffers witha bypass path coupled to the horizontal and vertical segments that gothrough switching matrices. Also, provision is made through theinterconnect to supply control signals to all CLBs in the array from asingle source.

The configurable logic blocks, according to the present invention, arecharacterized by a number of improvements over the prior art. Inparticular, the configurable logic blocks provide for a mixture ofnarrow gating and wide gating functions, which suffer a speed penaltyonly for the wide gating functions. Also, the configurable logic blocksare symmetrical, accepting inputs on four sides of each block andproviding outputs on four sides. The output structures themselvesprovide the ability for tristating outputs connected to the configurableinterconnect, and for directly driving signals to other configurablelogic blocks.

The input structures on all four sides of the configurable logic blocksare independently configurable in response to the configuration program.Likewise, the four output macro cells in each configurable logic blockare independently configurable.

As a feature that allows greater utilization of resources on the array,the registers in each of the output macro cells are accessibleindependently of the combinational logic in the configurable logicblock. This allows these registers to be used in networks that areindependent of the combinational logic.

According to one aspect, the configurable logic block can becharacterized as having an input multiplexing tree which receives Jinput signals and selects a subset K signals, where K is less than orequal to J, in response to the program data. Combinational logic iscoupled to the configuration memory and the input multiplexing tree, forgenerating a plurality of L logic signals in response to the K signalsand the program data. Four independent output macro cells are included,each of which select output signals from the plurality of L logicsignals.

Each of the output macro cells includes a tristatable output buffer fordriving a selected output signal to the configurable interconnect. Also,each output macro cell includes a second output buffer, for driving asignal that is selected independently of the tristatable output buffer,for driving signals onto direct connections to other configurable logicblocks.

The input multiplexing tree is characterized by providing that any oneof the K signals can be supplied from any of the four sides of theconfigurable logic block.

The combinational logic is implemented with a first lookup table in theprogram data consisting of 64 bits which are grouped into eight 8 bitarrays. The 8 bit arrays are paired so that three independently suppliedsignals from the subset of K signals supplied by the input multiplexingtree are used to address each of the four pairs of 8 bit arrays. The twooutputs of each pair are coupled to a cross-multiplexer which isconfigurable in response to the program data to directly pass throughthe two outputs supplied by the two 8 bit arrays in the pair, or toselect one of the two outputs as a primary output in response to afourth independently supplied signal from the subset K signals. Theoutput of the cross-multiplexer is supplied through a third multiplexinglevel consisting of two multiplexers, each independently controllable byrespective ones of the subset of K signals. The output of the thirdlevel of multiplexing is then supplied to a fourth level of multiplexingwhich is controlled by one of the subset of K signals, providing outputwhich is a full lookup function of the 64 bit array in response to sixinputs.

The combinational logic further includes a special 16 bit array in theprogram data which is coupled to a sixteen to one multiplexer. Controlinputs to the sixteen to one multiplexer are the pass through outputs ofthe four cross-multiplexers referred to above. Each of these inputs is afunction of four independent variables. The output of the sixteen to onemultiplexer provides a special output, which provides a limited lookupfunction of the 16 independent variables. The special output is combinedwith the output of the fourth level multiplexer in a fifth levelmultiplexer, which is controlled in response to an input signal of thesubset of K signals, or by the program data.

According to another aspect, the configurable logic block ischaracterized by a preload capability. During programming of theconfigurable logic array, each of the storage elements in the outputmacro cells of the configurable logic blocks is enabled to receive dataas if it were a location in the configuration memory.

The configurable input/output architecture, according to the presentinvention, is characterized by a number of improvements over the priorart. In particular, the architecture provides for groups of input/outputblocks associated with each row and column of configurable logic blocksin the array. Each of the groups is further characterized by having aplurality of complex input/output blocks, which provide flexiblestructures for implementing interfaces between the configurable logicarray and outside devices, and at least one simple input/output blockwhich provides a fast path from outside the device to the configurablelogic array if required by a particular application.

Further, both the simple and complex input/output blocks arecharacterized by having at least one tristatable output buffer fordriving signals onto the configurable interconnect structure, and asecond buffer for driving direct connections to configurable logicblocks in the device.

The complex input/output blocks include an input storage element and anoutput storage element. A direct connection is provided from the inputstorage element of one complex input/output cell to a next adjacentcomplex input/output around the perimeter of the device. The outputstorage elements of the complex input/output cells are similarlyconnected. Thus, the storage elements in the complex input/output blockscan be linked into a configurable data path where they can be operatedas a shift register or other similar circuit.

The storage elements in the complex input/output blocks are furtherconfigured to provide for synchronization functions, local readbackfunctions, and buried register functions.

The input/output blocks, according to the present invention, are furthercharacterized by control signal generation from the long lines in theprogrammable interconnect structure. This allows utilization of networksin the configurable logic array to control the operation andconfiguration of the configurable input/output blocks in a dynamicfashion. Also, the long lines are configured to propagate signalscompletely around the perimeter of the array, so that a common signalcan be used to control all of the input/output blocks.

The configurable logic array provided, according to the presentinvention, greatly improves the flexibility and performance ofprogrammable gate arrays over those available in the prior art. This isaccomplished in part by an interconnect structure which supportsnetworks with long reach across the device, multi-source networks, andsymmetrical connections to the configurable logic blocks.

Further, a unique configurable logic block architecture supportsefficient utilization of the resources in the array, wide gatingfunctions, narrow gating functions without speed penalty andimplementation of symmetrical networks in the array.

Finally, a unique input/output architecture supports efficientutilization of the resources in the input/output structures, allows forboth fast signal propagation through the simple input/output blocks andhigh function signal propagation through the complex input/output blocksinto the array, and has improved flexibility in the source of controlsignals for the input/output structure.

Further aspects and advantages of the present invention will be foundupon review of the drawings, the detailed description and the claimswhich follow.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is schematic diagram illustrating the layout of the programmablegate array according to the present invention.

FIG. 2 is a schematic diagram of the configuration memory in theprogrammable gate array according to the present invention.

FIG. 3 is a diagram of the configuration memory storage cell.

FIG. 4 illustrates a notation scheme for vertical buses in theprogrammable gate array.

FIG. 5 illustrates a notation scheme for the horizontal buses in theprogrammable gate array.

FIG. 6 illustrates the placement of the switch matrices in lines 5-14 ofthe horizontal and vertical buses in the programmable gate array.

FIG. 7 illustrates the intersection of a vertical bus with a horizontalbus.

FIG. 8 illustrates an alternative intersection of a vertical bus with ahorizontal.

FIG. 9 illustrates the intersection of vertical buses 1 and 9 with evennumbered horizontal buses and horizontal buses 1 and 9 with evennumbered vertical buses.

FIG. 10 illustrates the intersection of vertical buses 1 and 9 with theodd numbered horizontal buses and horizontal buses 1 and 9 with the oddnumbered vertical buses.

FIG. 11 illustrates the intersection of horizontal bus 1 with verticalbus 1 at the corner.

FIG. 12 illustrates the intersection of horizontal bus 1 with verticalbus 9 at the corner.

FIG. 13 illustrates the intersection of horizontal bus 9 with verticalbus 1 at the corner.

FIG. 14 illustrates the intersection of horizontal bus 9 with verticalbus 9 at the corner.

FIG. 14A illustrates an alternative corner connection scheme that can beused at all four corner intersections, replacing the schemes of FIGS.11-14.

FIG. 15 illustrates the connection of lines 16 and 17 of the verticalbuses with the global reset and global clock buffers.

FIG. 15A illustrates the connection of the vertical lines 16 and 17 withthe configurable logic blocks.

FIG. 15B illustrates the signal path from an input/output pad bypassinginternal IOB logic for connection to the global clock buffer, horizontalalternate buffer or vertical alternate buffer.

FIG. 15C illustrates the inputs to the global clock buffer.

FIG. 16 illustrates the connection of the horizontal alternate bufferswith line 15 on the horizontal buses and the vertical alternate bufferswith line 15 on the vertical buses

FIG. 16A illustrates the connection of the input/output blocks and theconfigurable logic blocks with line 15.

FIG. 16B illustrates the input paths to the vertical alternate buffer.

FIG. 16C illustrates the input paths to the horizontal alternate buffer.

FIG. 16D illustrates the crystal oscillator circuit by which theoscillator signal OSC is generated on the chip.

FIG. 16E illustrates the external connections for the oscillator of FIG.16D.

FIG. 17 illustrates one implementation of a programmable interconnectpoint using bidirectional pass transistors.

FIG. 18 illustrates an alternative configuration of a programmableinterconnect point using a unidirectional multiplexer technique.

FIG. 19 illustrates the interconnect structure of the switch matrix.

FIG. 20 illustrates the repowering buffer used in the programmableinterconnect.

FIG. 21 shows the switch matrix interconnection options for eachconnection to the switch matrix.

FIG. 22 illustrates the interconnection in the segment boxes on verticalbuses 1 and 9.

FIG. 23 illustrates the interconnection in the segment boxes onhorizontal buses 1 and 9.

FIG. 24 illustrates the segment box interconnection options for eachconnection to the segment box.

FIG. 25 is an overview block diagram of the configurable logic block.

FIG. 26 schematically illustrates the inputs and outputs and provides anotation for the configurable logic block.

FIG. 27 is a schematic diagram of the combinational logic in theconfigurable logic block.

FIG. 28 is a schematic diagram of the special output stage which iscoupled to the combinational logic of FIG. 27.

FIG. 29 is a schematic diagram of the macro cell for outputs X1 and Y1on the configurable logic block.

FIG. 29A illustrates the connection of the register in the macro cellwhich provides for preload during programming of the configurable logicarray.

FIG. 30 is a schematic diagram of the macro cell for outputs X2 and Y2on the configurable logic block.

FIG. 31 is a schematic diagram of the macro cell for outputs X3 and Y3on the configurable logic block.

FIG. 32 is a schematic diagram of the macro cell for outputs X4 and X4on the configurable logic block.

FIG. 33 is a diagram of the input multiplexing structure for signalsVA1-VA4 which are used in the first level multiplexing in thecombinational logic section of the configurable logic block.

FIG. 34 is a schematic diagram of the input multiplexing structure forsignals VB1-VB4 which are used in the first level multiplexing in thecombinational logic section of the configurable logic block.

FIG. 35 is a schematic diagram of the input multiplexer structure forsignals VC1-VC4 which are used in the first level multiplexing in thecombinational logic section of the configurable logic block.

FIG. 36 is a schematic diagram of the input multiplexing structure forsignals VD1-VD4 which are used in the second level multiplexing in thecombinational logic section of the configurable logic block.

FIG. 37 is a diagram of the input multiplexing structure for VE1 and VE2used in the third level multiplexing of the combinational logic.

FIG. 38 is a diagram of the input multiplexing structure for the fourthlevel multiplexing signal VF in the combinational logic.

FIG. 39 is a schematic diagram of the input multiplexing structure forthe control signal VG used in providing the special output.

FIGS. 40A-40H show respectively the input multiplexing for the generalpurpose control lines CT1-CT8.

FIG. 41 is a schematic diagram of the circuit generating output enablecontrol signals OE1-OE4 in the configurable logic block.

FIG. 42 is a diagram illustrating selection of the clock signal in theconfigurable logic block.

FIG. 43 is the schematic diagram illustrating generation of the clockenable signal in the configurable logic block.

FIG. 44 is a schematic diagram illustrating selection of the resetsignal in the configurable logic block.

FIG. 45 is a schematic diagram of a simple input/output cell accordingto the present invention.

FIG. 46 is a schematic diagram of a complex input/output cell accordingto the present invention.

FIG. 47 illustrates the inputs and outputs of the complex input/outputblock.

FIG. 48 illustrates the inputs and outputs of the simple input/outputblock.

FIG. 49 schematically illustrates the connection of the complexinput/output blocks in a shift register configuration.

FIG. 50 illustrates the direct connections from outputs of next adjacentconfigurable logic blocks to the inputs of a given logic block.

FIG. 51 illustrates direct connections from adjacent configurable logicblocks to the inputs of the center configurable logic block.

FIG. 52 illustrates direct connections from the output of the centerconfigurable logic block to adjacent and next adjacent configurablelogic blocks.

FIG. 53 illustrates direct connection of the outputs X1-X4 on peripheralconfigurable logic blocks.

FIG. 54 illustrates direct connection to the inputs of a peripheralconfigurable logic block.

FIG. 55 illustrates direct connections to the inputs F1-F4 on aperipheral configurable logic block.

FIG. 56 illustrates the programmable connections between theinterconnect structure and the configurable logic blocks.

FIG. 57 illustrates the fixed connections between the interconnectstructure and the configurable logic blocks.

FIG. 58 illustrates the programmable connection of the configurablelogic blocks in the array to uncommitted long lines.

FIG. 59 illustrates the programmable connections to the outer long linesfrom the CLBs.

FIG. 60 illustrates the reach between input/output blocks andconfigurable logic blocks on long lines.

FIG. 61 illustrates the programmable connections between theinput/output blocks on the top side of the configurable array andhorizontal bus 1.

FIG. 62 illustrates the programmable connections between horizontal bus9 and the input/output blocks on the bottom side of the configurablearray.

FIG. 63 illustrates the programmable interconnects between the verticalbus 1 and the input/output blocks on the left side of the array.

FIG. 64 illustrates the programmable interconnects between vertical bus9 and the input/output blocks on the right side of the array.

FIG. 65 illustrates the connection of the clock and reset signals to thecomplex logic blocks, as well as the programmable connections of theinputs and the outputs of the input/output blocks on the top side of thearray to the vertical buses.

FIG. 66 illustrates the connection of the clock and reset signals to theinput/output blocks on the bottom side of the array, and connection ofthese bottom side input/output blocks to the vertical buses.

FIG. 67 illustrates the connection of the clock and reset signals to theinput/output blocks on the left side, and connection of these left sideinput/output blocks to horizontal buses.

FIG. 68 illustrates the connection of the clock and the reset signals tothe input/output blocks on the right side of the array, and connectionof these right side input/output blocks to the horizontal buses.

FIG. 69 illustrates the connection of the control signal inputs on theinput/output blocks on the top and left side of the array to theadjacent interconnect buses.

FIG. 70 illustrates the connection of the control signal inputs to theinput/output blocks on the right and bottom side of the array to theadjacent interconnect buses.

DETAILED DESCRIPTION

With reference to the figures, a detailed description of a preferredembodiment of the present invention is provided.

First, with reference to FIGS. 1-3, the basic layout and programmingstructure of the programmable gate array is described. Next, a detaileddescription of the interconnect structure is set out with reference toFIGS. 4-24. Implementation of the configurable logic block utilized inthe programmable gate array is described with reference to FIGS. 25-44.Implementation of the configurable logic blocks utilized in theprogrammable gate array are described with reference to FIGS. 45-49.

After description of the configurable logic blocks and the input/outputcells, the direct connections among the input/output blocks and theconfigurable logic blocks are described with reference to FIGS. 50-55.This is followed by a description of the connections of the configurablelogic blocks and input/output cells to the rest of the interconnectstructure with reference to FIGS. 56-70.

I. Layout and Programming Structure

FIG. 1 illustrates the layout of the programmable gate array accordingto the present invention. Also provided in FIG. 1 is a notation which isutilized to describe the programmable gate array in this application.Accordingly, the programmable gate array shown in FIG. 1 consists of anarray of configurable logic blocks illustrated by the square symbol withbold lines shown at the upper left hand corner of the figure. Eachconfigurable logic block in the array is labeled with a row and columnnumber, i.e. in the upper left hand corner of the array, theconfigurable logic blocks are labeled R1C1, R1C2, and so on until thelower right hand corner of the array where the configurable logic blockis labeled R8C8.

Around the peripheral of the array are 110 pads for connection toexternal pins. Pads 2-13, 16-27, 29-40, 43-54, 57-68, 71-82, 85-96 and99-110 are coupled to configurable input/output blocks represented bythe symbol shown in the upper left hand corner of the figure. Pads 1,14, 15, 28, 41, 42, 55, 56, 69, 70, 83, 84, 79 and 98 are utilized forfunctions other than configurable input/output blocks, such as power,ground, global clock and reset signal inputs, and programming modecontrol signals. The connection of these miscellaneous pads is similarto that done in prior art programmable gate array and is not furtherdescribed here.

The interconnect structure consists of nine horizontal buses labeledHBUS1 through HBUS9 with nine intersecting vertical buses VBUS1 throughVBUS9. The intersections of vertical bus 1 and vertical bus 9 with thehorizontal buses 2-8 are characterized by having segment boxes whichprovide programmable interconnection between the respective horizontalbus and the vertical bus as described in detail below. Likewise, theintersections of horizontal bus 1 and horizontal bus 9 with verticalbuses 2-8 are characterized by segment boxes providing the programmableinterconnection between the horizontal and vertical buses.

The intersections of the vertical buses 2-8 with the horizontal buses2-8 are characterized by switching matrices providing forinterconnection between the respective horizontal and vertical buses.The placement of the segment boxes and switching matrices isschematically illustrated in FIG. 1 using the symbols illustrated in thelower left hand corner of the figure. The detailed structure of theswitching matrices and segment boxes is described below.

The programmable gate array according to the present invention containsthree types of configurable elements that are customized to a usersystem design which is specified in a configuration memory. The threeconfigurable elements are the array of configurable logic blocks (CLBs),the configurable input/output blocks (IOBs) around the perimeter, andthe programmable interconnect network.

The system design of a user is implemented in the programmable gatearray by configuring programmable RAM cells known as a configurationmemory. These RAM cells control the logic functionality performed by theCLBs, IOBs, and the interconnect. The loading of the configurationmemory is implemented using a set of design software tools as well knownin the art.

The perimeter of configurable IOBs provide a programmable interfacebetween the internal logic array and device package pins. The array ofCLBs perform user specified logic functions. The interconnectionconsists of direct connections between specific CLBs or IOBs, and ageneral connect that is programmed to form networks carrying logicsignals among the blocks.

The logic functions performed by the CLBs are determined by programmedlookup tables in the configuration memory. Functional options areperformed by program controlled multiplexers. Interconnecting networksbetween blocks are composed of metal segments joined by programmableinterconnect points (PIPs).

The logic functions, functional options, and interconnect networks areactivated by a program data which is loaded into an internal distributedarray of configuration memory cells. The configuration bit stream isloaded in to the device at power up and can be reloaded on command.

FIG. 2 is a schematic diagram of the programmable gate array as seen bythe program data. The programmable gate array includes a plurality ofdistributed memory cells referred to as the configuration memory 200.Program data on line 201 is loaded into shift register 202 in responseto a clock signal on line 203. The detect logic 204 determines when theshift register is full by reading a preamble from data on 201. When theshift register is full, the detect logic 204 signals across line 205 aframe pointer logic 206 which generates frame pointer signals acrosslines 207. Control logic 208 is responsive to the mode inputs to thedevice on line 209 to control the detect logic 204 across line 210 andthe frame pointer during loading of the configuration memory 200.

The configuration memory 200 is organized into a plurality of framesF1-FN. As program data is loaded into the shift register, the framepointer F1 is activated to load the first frame in the configurationmemory. When the shift register is loaded with the second frame of data,the frame pointer for F2 is activated, loading the second frame F2, andso on until the entire configuration memory is loaded. Control logic 208generates a program done signal on line 210.

The static memory cell used in the configuration memory is shown in FIG.3. It has been specially designed for high reliability and noiseimmunity. A basic cell 300 consists of a data input line 301 coupled topass transistor 302. The gate of the pass transistor 302 is coupled to aread or write control signal on line 303. The output of the passtransistor 302 is coupled to line 304. Line 304 is coupled to the inputof inverter 305 and to the output of inverter 306. The output ofinverter 305 is coupled to line 307 which is coupled back to the inputof inverter 306. Lines 304 and 307 provide Q and Q outputs forconfiguration control. Thus, the basic cell 300 consists of two CMOSinverters and a pass transistor. The pass transistor is used for writingand reading cell data. The cell is only written during configuration andonly read during read-back in the programming mode. During normaloperation, the pass transistor is off and does not affect the stabilityof the cell. The memory cell outputs Q and Q use full ground and V_(CC)levels and provide continuous direct control.

The configuration store can also be implemented with other types ofvolatile or non-volatile storage cells. For instance, non-volatilememory, like EPROM, E² PROM, programmable resistive links, or Ferro RAM,could be used.

The device memory is configured as mentioned above by downloading a bitstream from a host system or an external memory, such as an EPROM. Theconfiguration processes are the same as those used in prior artprogrammable gate array, with one exception which is discussed belowwith reference to the configurable logic blocks.

II. The Configurable Interconnect Structure

Horizontal and vertical buses of the interconnect structure and theinterconnection of the horizontal and vertical buses are described withreference to FIGS. 4-24.

FIG. 4 illustrates the notation used for the vertical buses. Eachvertical bus has 25 lines. Lines 1-4 and 15-17 are long lines which runacross the entire array. Lines 5-14 consist of bidirectional generalinterconnect segments which are coupled through switching matrices andsegment boxes as described below. Lines 18-25 are uncommitted long lineswhich run the entire length of the array.

FIG. 5 illustrates the notation used for the horizontal buses. Eachhorizontal bus is a 23 line bus in which lines 1-4 and 15 are longlines, lines 5-14 are bidirectional general interconnect segments, andlines 16-23 are uncommitted long lines. The distinctions between thelong lines, the bidirectional general interconnect segments, and theuncommitted long lines are set out in detail below.

In order to construct networks through a device, the horizontal andvertical buses require means of interconnection. This occurs at theintersections of the horizontal buses and the vertical buses. Theinterconnections between the lines at the intersection are made throughprogrammable interconnect points, switch matrices, and segment boxes.

FIG. 6 illustrates the placement of the switch matrices in theinterconnect structure.

With reference to FIG. 1, it can be seen that the switch matrices arepositioned at the intersections of vertical bus 2-8 with horizontalbuses 2-8. FIG. 6 illustrates the placement of the switch matrices onhorizontal bus 4 adjacent the configurable logic block R3C3, R3C4, R4C3,and R4C4. It can be seen that the switch matrices are positioned only onlines 5-14 of the bidirectional general interconnect structure. Thus,the bidirectional general interconnect structure consists of segmentswhich are two configurable logic blocks in length, spanning, in thiscase, from switch matrix 600, located on vertical bus 3, to switchmatrix 601, located on vertical bus 5 in lines 5-9 of a bidirectionalgeneral interconnect. Switch matrix 602 is coupled to segments of line10-14 which extend from vertical bus 2 to vertical bus 4 and verticalbus 4 to vertical bus 6. Vertical buses 2 and 6 are not shown in FIG. 6.

Using the switch matrix placement as shown in FIG. 6 and in FIG. 1, itcan be seen that a connection to a bidirectional general interconnectallows propagation of the signal across a width equal to twoconfigurable logic blocks on the array without passing through a switchmatrix. This allows networks with fewer delays due to switch matrices.

FIGS. 7 and 8 illustrate the complete intersection between verticalbuses 2-8 and horizontal buses 2-8, where a circle indicates abidirectional programmable interconnect point controlled by a memorycell in the configuration memory.

FIG. 7 is the structure for the intersection of odd numbered verticalbuses with odd numbered horizontal buses, and even numbered verticalbuses with even numbered horizontal buses. FIG. 8 is the structure forthe even-odd and odd-even intersections between vertical and horizontalbuses.

It can be seen that in FIG. 7, horizontal line 1 is connectable tovertical lines 1 and 4. Horizontal line 2 is connectable to verticallines 2 and 3. Horizontal line 3 is connectable to vertical lines 2 and3. Horizontal line 4 is connectable to vertical lines 1 and 4.

Horizontal lines 5-9 are coupled to the left side 700 of a switchmatrix. The right side 701 of the switch matrix provides line 5 which isconnectable to vertical line 14. The horizontal line 6 output from theright side 701 of the switch matrix is connectable to vertical line 13.Horizontal line 7 from the switch matrix is coupled through aprogrammable interconnection point (PIP) to vertical line 12. Horizontalline 8 from the switch matrix side 701 is coupled through PIP tovertical line 11. Horizontal line 9 output from the right side 701 ofthe switch matrix is coupled through a PIP to vertical line 10.

The bidirectional general interconnect segments 10-14 of the horizontalbus are connectable through PIPs to the bidirectional generalinterconnect segments in the vertical bus lines 5-9 and 10-14 in theconfiguration shown. Lines 10-13 of the horizontal bus bidirectionalsegments are connectable to the odd numbered uncommitted long lines 19,21, 23 and 25 through PIPs as shown.

The horizontal long line 15 passes through the intersection withoutbeing connectable to any other line.

The odd numbered uncommitted long lines 17, 19, 21, and 23 in thehorizontal bus are connectable through PIPs to the verticalbidirectional interconnect segments 10-13 as shown.

The interconnection of the even or odd numbered vertical buses with oddor even numbered horizontal buses, respectively, is shown in FIG. 8. Aswith the intersection shown in FIG. 7, the horizontal lines in theintersection structure of FIG. 8 are connectable through PIPs and theswitch matrix to the vertical lines.

Horizontal long line 1 is connectable to vertical lines 1 and 4.Horizontal long line 2 is connectable to vertical lines 2 and 3.Horizontal long line 3 is connectable to vertical long lines 2 and 3.Horizontal long line 4 is connectable to vertical long lines 1 and 4.

Horizontal bidirectional general interconnects 5-9 are connectable tothe bidirectional general interconnects 5-14 as shown in the figure andto the even numbered uncommitted long lines 18, 20, 22, and 24. Thebidirectional general interconnects 10-14 are connectable to thevertical bidirectional general interconnects 5-9 and through theswitching matrix to the adjacent segments of lines 10-14 in both thevertical and the horizontal buses. The even numbered uncommitted longlines 16, 18, 20, and 22 on the horizontal bus are connectable to thevertical bidirectional segments 6-9 as shown.

FIG. 9 illustrates the intersection of horizontal buses 1 and 9 with theeven numbered vertical buses 2-8 and vertical buses 1 and 9. FIG. 10illustrates the intersection of the horizontal buses 1 and 9 with theodd numbered vertical buses 3-7.

Thus, the horizontal long lines 1-4 are connectable to vertical longlines 1-4 as shown. The bidirectional general interconnect lines 5-9 areconnectable through the segment box to vertical interconnects 5-9. Thebidirectional general interconnects 10-14 are connectable to verticalbidirectional general interconnects 10-14. Also, the bidirectionalgeneral interconnects 10-13 are connectable to the odd numbereduncommitted long lines 19, 21, 23, and 25.

The odd numbered uncommitted long lines 17, 19, 21, and 23 on thehorizontal bus are connectable to the bidirectional general interconnectsegments 10-13 as shown.

In the intersection shown in FIG. 10, long lines 1-4 on the horizontalbus are connectable respectively to vertical lines 1-4. Thebidirectional general interconnect segments 5-9 are connectable to thevertical segments 5-9 and to the even numbered uncommitted long lines18, 20, 22, and 24 as shown. The horizontal bidirectional generalinterconnect segments 10-14 are connected to the segment box in both thehorizontal and vertical directions. The even numbered uncommitted longlines 16, 18, 20, and 22 on the horizontal bus are connectable tovertical bidirectional general interconnect segments 6-9 as shown.

The corner intersections are shown in FIGS. 11-14. FIG. 11 illustratesthe intersection of horizontal bus 1 with vertical bus 1. As shown, thelines 1-14 in the horizontal bus are connectable respectively to lines1-14 in the vertical bus. The even numbered uncommitted long lines 18,20, 22, and 24 on the vertical bus are connectable to horizontalbidirectional general interconnect segments 6-9. The even numbereduncommitted long lines 16, 18, 20, and 22 on the horizontal bus areconnectable to the vertical lines 6-9.

FIG. 12 illustrates the intersection of horizontal bus 1 with verticalbus 9. In this instance, the horizontal line 1 is connectable tovertical lines 1 and 4. Horizontal line 2 is connectable to verticallines 2 and 3. Horizontal lines 13-14 are connectable respectively tovertical lines 3-14. The even numbered uncommitted long lines 18, 20,22, and 24 on the vertical bus are connectable to horizontal lines 6-9.The even numbered uncommitted long lines 16, 18, 20, and 22 on thehorizontal bus are connectable to the vertical lines 6-9.

FIG. 13 illustrates the intersection of horizontal bus 9 with verticalbus 1. The horizontal lines 1-14 are connectable to the vertical lines1-14, respectively. Also, horizontal line 3 is connectable to verticalline 2 and horizontal line 4 is connectable to vertical line 1. Thehorizontal lines 6-9 are also connectable to the even numbereduncommitted long lines 18, 20, 22 and 24 on the vertical bus. The evennumbered uncommitted long lines 16, 18, 20 and 22 on the horizontal busare connectable to vertical lines 6-9.

FIG. 14 illustrates the intersection of horizontal bus 9 with verticalbus 9. Horizontal lines 1-14 are connectable to vertical lines 1-14,respectively. Horizontal lines 6-9 are also connectable to the evennumbered uncommitted long lines 18, 20, 22 and 24 on the vertical bus.The even numbered uncommitted long lines 16, 18, 20 and 22 on thehorizontal bus are connectable to vertical lines 6-9.

FIG. 14A shows a corner connection that can be used at the intersectionsof horizontal bus 1 and vertical bus 1, horizontal bus 1 and verticalbus 9, horizontal bus 9 and vertical bus 9, and horizontal bus 9 andvertical bus 1. It has the advantage that it is a single layout that canbe used at all four corners while accomplishing the ability to routesignals from the long lines 1-4 completely around the perimeter of thechip. As can be seen, horizontal lines 1-14 are connectable to verticallines 1-14, respectively. Horizontal line 1 is connectable to verticalline 4, horizontal line 2 is connectable to vertical line 3, horizontalline 3 is connectable to vertical line 2, and horizontal line 4 isconnectable to vertical line 1. Also, horizontal line 14 is connectableto vertical line 5, horizontal line 13 is connectable to vertical line6, horizontal line 12 is connectable to vertical line 7, horizontal line11 is connectable to vertical line 8, horizontal line 10 is connectableto vertical line 9, horizontal line 9 is connectable to vertical line10, horizontal line 8 is connectable to vertical line 11, horizontalline 7 is connectable to vertical line 12, horizontal line 6 isconnectable to vertical 13, and horizontal line 5 is connectable tovertical line 14. Also, horizontal lines 6-9 are connectable to the evennumbered, uncommitted long lines 18, 20, 22, and 24 on the vertical bus.The even numbered long lines 16, 18, 20, 22 on the horizontal bus areconnectable to vertical lines 6-9.

Lines 15 on the horizontal and vertical buses and 16 and 17 on thevertical buses are not connectable at any of the intersections describedabove. Rather, they are designed to be used for local clock/clockenable, global clock, and global reset signals and have specialconnection structures shown in FIGS. 15 and 16. FIG. 15 illustrates theconnection of the global clock and global reset signals on verticallines 16 and 17. The global clock signal is supplied from an inputbuffer 1500 to line 1501. Line 1501 is directly connected to line 16 inall vertical buses. Similarly, the global reset signal is supplied atglobal reset buffer 1502. The output of the global reset buffer issupplied on line 1503 to line 17 on all the vertical buses. The lines 16and 17 of the vertical buses are directly connected to the input/outputblocks as schematically illustrated in FIG. 15 and to each of theconfigurable logic blocks. The direct connections to the configurablelogic blocks are shown only to a few of the blocks in the upper lefthand corner of the array for clarity of the figure.

FIG. 15A shows the connection of lines 16 and 17 of the vertical busesto the configurable logic blocks. The lines 16 and 17 of vertical bus-nare coupled to the global clock GK and global reset GR inputs ofconfigurable logic block in column n, for n=1-8. In vertical bus 9,lines 16 and 17 are connected only to the input/output blocks as shown.

FIG. 15B shows the configurable path from an input/output pad to an IOBor to the global or alternate buffers. It can be seen that the pad 1510is connected across line 1511 through buffer 1512 to line 1513. Line1513 is passed through pass transistor 1514 to an IOB input path 1515 orthrough pass transistor 1516 to the buffer input circuitry on line 1517.A memory cell 1518 in the configuration store controls which passtransistor (1514 or 1516) is enabled.

FIG. 15C illustrates the input circuitry to the global clock buffer.Input I of IOB 2 and 9 are connected to provide a signal on lines 1518and 1519 as inputs to 8 to 1 multiplexer 1521. A clock input pin at IOB110 is connected to line 1520 as illustrated in FIG. 15B as input tomultiplexer 1521. Lines 14 and 15 in vertical bus 1 and lines 14 and 15in horizontal bus 1 are also coupled as inputs to configurablemultiplexer 1521.

The direct connect output X4 on the configurable logic block in row 1,column 1 is directly connected as well as an input to the multiplexer1521. The direct link from an adjacent CLB to the multiplexer 1521across line 1524 provides added flexibility for the generation of theglobal clock on chip.

The configuration store controls the multiplexer 1521 to supply a clocksignal on line 1522 to the global clock buffer 1523.

FIG. 16 illustrates the connection of line 15 in the vertical andhorizontal buses. It is designed to perform the function of a localclock for an input/output block or a configurable logic block or as aclock enable signal. The line 15 in horizontal buses is connectable to avariety of sources including outputs from configurable logic blocks andthe alternate buffers. The line 15 in the horizontal buses areconnectable to the horizontal alternate buffer 1600 which generates thesignal on line 1601. Associated with each horizontal bus is abidirectional buffer, such as buffer 1602. Each bidirectional bufferincludes a configurable tristate buffer connected from line 1601 to line15 in the respective horizontal bus. Also, a configurable tristatebuffer connected from line 15 on the respective horizontal bus suppliesan output to line 1601. The configurable tristate buffers are eachcontrolled by a memory cell in the configuration memory.

Likewise, the vertical alternate buffer 1603 generates a signal on line1604. Line 15 on each vertical buffer is connected to a bidirectionalbuffer, e.g. buffer 1605. Each bidirectional buffer has a first tristatebuffer connected from line 1604 to line 15 in the respective verticalbus and a tristate buffer connected from line 15 in the respectivevertical bus to line 1605. Each of the tristate buffers is controllablefrom a storage cell in the configuration memory. The line 15's invertical buses 1 and 9 are connected respectively to the input/outputblocks on the left side and right side of the chip. Likewise, the line15's in horizontal buses 1 and 9 are connected to the input/outputblocks on the top and bottom of the chip as shown.

FIG. 16A shows the connection of the input/output blocks to line 15 andthe connection of the configurable logic blocks to line 15. Each complexIOB 1606 has a K input directly connected to line 15 on its adjacentvertical or horizontal bus. Each simple IOB 1607 is capable of supplyingan input signal to line 15 of a horizontal and vertical bus through aPIP.

Each configurable logic block as shown in FIG. 16A has inputs labeledK1, K2, K3 and K4. The input K1 is connected to line 15 in thehorizontal bus above the block. Input K2 is directly connected to line15 in the vertical bus to the right of the block. Input K3 is directlyconnected to line 15 in the horizontal bus below the block. Input K4 isdirectly connected to the vertical bus to the left of the block.Likewise, each configurable logic block has output Y1, Y2, Y3 and Y4.The output Y1 is connectable through a PIP to line 15 in the horizontalbus above the block. Output Y2 is connectable through a PIP to line 15in the vertical bus to the right of the block. Output Y3 is connectablethrough a PIP to line 15 in the horizontal bus below the block. OutputY4 is connectable through a PIP to line 15 in the vertical bus to theleft of the block.

The line 1604 connected to the vertical alternate buffer and the line1601 connected to the horizontal alternate buffer can receive inputsfrom a number of sources including device pins, and interconnects viaPIPs. The signal on line 1601 can be supplied to all configurable logicblocks and input/output blocks adjacent the horizontal buses with theexception of input/output blocks on the left side and right side of thechip. Likewise, the signal on line 1604 can be globally supplied acrossthe chip, with the exception that it cannot be directly connected to theinput/output blocks on the top and bottom of the chip.

Therefore, a signal can be generated in configurable logic block R1C1,supplied to line 15 of vertical bus 2 through the bidirectional buffer1608 to line 1604. From line 1604, it can be supplied anywhere in thechip. A similar net can be formed along horizontal buses.

This line 15 structure allows the registers in any configurable logicblock to receive a clock from one of five sources. The sources includethe global clock GK supplied on vertical bus line 16, and the localclocks K1, K2, K3, and K4 which are connected to line 15 on fouradjacent interconnect buses.

Likewise, the registers in a complex input/output block can receive aclock from two sources. The first source is line 16 in the adjacentvertical bus at its GK input and from an input K on the configurable I/Oblock connectable through a PIP to line 15 on either a horizontal orvertical bus depending on the location of the input/output block.

Each line 15 in either a horizontal or a vertical bus can carry a signalobtained from one of four sources. The four sources include an alternatebuffer, an adjacent configurable logic block, an adjacent input/outputblock, and a configurable logic block which has supplied a signal toline 15 of a different bus which has in turn been connected through thebidirectional buffers to levels 1601 or 1604.

If an alternate buffer is used to supply a signal to the array, the longlines connecting to that buffer can either be independent where thebidirectional buffers are configured to supply a high impedance state tothe long line, or they can use the alternate buffer as a source.

FIG. 16B illustrates the input structure to the vertical alternatebuffer 1603. The input to the vertical alternate buffer 1603 is providedon line 1610 at the output of the configurable multiplexer 1611. Also,the signal on line 1610 is connected for supply as output signals at IOB1612 and at IOB 1613. Inputs to the multiplexer 1611 include anoscillator signal OSC as generated by the circuitry illustrated in FIGS.16D and 16E. Also, an input signal from IOB 1612 is an alternative inputto multiplexer 1611 across line 1614. A vertical clock input signal issupplied on line 1615 as input to multiplexer 1611 from IOB 1616configured as shown in FIG. 15B.

Long lines 5 and 15 of the vertical bus 9 and long lines 5 and 15 of thehorizontal bus 9 are also connected as inputs to multiplexer 1611. Thefinal input to multiplexer 1611 is a direct link from output X2 of theconfigurable logic block in row 8, column 8, across line 1617.

The vertical alternate buffer 1603 also includes a memory cell 1618 fortristate control.

FIG. 16C illustrates the input structure for the horizontal alternatebuffer 1600. The horizontal alternate buffer is tristatable in responseto the signal at memory cell 1620. The input to horizontal alternatebuffer 1600 is supplied on line 1621 at the output of the configurablemultiplexer 1622. Inputs to the configurable multiplexer 1622 includethe horizontal clock input signal on line 1623, and input signals onlines 1624 and 1625 from input/output structures 1626 and 1627,respectively. The vertical bus lines 5 and 15 and horizontal bus lines 5and 15 are connectable as inputs as well to the multiplexer 1622.Finally, a direct link from the configurable logic block in row 8,column 1, output X4 is coupled across line 1628 as an input tomultiplexer 1622.

The on chip oscillator which supplies the OSC signal as one input to themultiplexer 1611 driving the vertical alternate buffer 1603 is shown inFIG. 16D. The OSC signal is provided at the output of multiplexer 1630which is controlled by memory cell 1631. Inputs to multiplexer 1630include the signal on line 1632 which is supplied at the output ofinverting buffer 1633. The input to inverting buffer 1633 is the signalon line 1634 which is supplied at the output of the oscillator amplifier1635. The input to the oscillator amplifier 1635 is supplied at IOB1636. IOB 1637 is coupled directly to line 1634. Line 1634 is suppliedthrough inverting buffer 1638 as a clock input on line 1639 to register1640. Register 1640 is connected as a divide-by-two circuit by couplingline coupled from its Q output through inverting buffer 1642 as the Dinput to register 1640. The Q output of register 1640 is supplied online 1643 as a second input to multiplexer 1630.

The external connections for the oscillator are shown in FIG. 16E. Pad1637 is coupled to line 1650 and pad 1636 is coupled to line 1651.Resistor R1 is connected between line 1650 and 1651. Line 1651 iscoupled through capacitor C1 to GROUND and through crystal 1652 to line1653. Line 1653 is coupled through capacitor C2 to GROUND and throughresistor R2 to line 1650.

The divide-by-two option in the oscillator circuit is provided to ensuresymmetry of the signal. The output of the 2:1 multiplexer 1630 givesthis choice, and is set during device configuration. When theoscillator/inverter is not used, the paths 1637 and 1636 areconfigurable as shown in FIG. 15B to behave as standard IOBs.

The oscillator circuit becomes active before configuration is completeto allow it to stabilize.

The structure of the programmable interconnect points (PIPs) is shown inFIG. 17 and an alternative structure is shown in FIG. 18. The structurein FIG. 17 illustrates that for an intersecting conductive segment, suchas long lines 1700 and 1701, with long line 1702, a PIP is implementedusing a pass transistor. Thus, pass transistor 1703 provides forinterconnection between lines 1702 and 1701. Pass transistor 1704provides for interconnection between lines 1700 and 1702. The memorycell 1705 from the configuration store controls the pass transistor 1703to provide a bidirectional path between the lines. Likewise, memory cell1706 controls pass transistor 1704 to provide the bidirectional path.These interconnection points are illustrated throughout this documentusing the circular symbol 1707 as shown in the figure. Thus, thesymbolic representation of the circuit on the left side of FIG. 17 isshown on the right side of FIG. 17.

The PIP implementation of FIG. 17 is advantageous in that it providesfor bidirectional connection on the lines which allows for greatflexibility. However, this structure is memory intensive. Therefore, analternative implementation, as shown in FIG. 18, can be used to savememory in a given implementation. The implementation of FIG. 18illustrates that a PIP can be implemented as a multi-source multiplexer1800. Multiplexer 1800 can have three sources, source 1, source 2, andsource 3, and select a destination line 1801 in response to memory cells1802 in the configuration store. Using the multiplexer implementation,two memory cells can provide for selection from among three or foursources. The equivalent symbol for the circuit using multiplexer 1800 isshown at 1803. It should be recognized that the multiplexerimplementation is a unidirectional interconnect which allows forconnection from any one of the source lines to the destination line andnot vice versa. Furthermore, only one source line can be activated for agiven operation.

FIG. 19 illustrates the implementation of the switch matrix according tothe present invention. Each switch matrix has five connections on thetop labeled 1-5, five connections on the right side labeled 6-10, fiveconnections on the bottom labeled 11-15, and five connections on theleft side labeled 16-20.

Line 1 is connectable through PIP 1-20 to line 20, through PIP 1-6 toline 6, through PIP 1-11 to line 11, and through PIP 1-15 to line 15.

Line 2 is connectable through PIP 2-19 to line 19, PIP 2-7 to line 7,PIP 2-14 to line 14, and PIP 2-15 to line 15.

Line 3 is connectable through PIP 3-18 to line 18, PIP 3-8 to line 8,PIP 3-13 to line 13, and PIP 1-14 to line 14.

Line 4 is connectable through PIP 4-17 to line 17, PIP 4-9 to line 9,PIP 4-12 to line 12, and PIP 4-13 to line 13.

Line 5 is connectable through 5-16 to line 16, PIP 5-10 to line 10, PIP5-11 to line 11, and PIP 5-12 to line 12.

Other than the bidirectional connections to lines 1-5 which have alreadybeen set out, the connections of lines 6-10 include the following.

Line 6 is connectable through PIP 6-15 to line 15, PIP 6-16 to line 16,and through PIP 6-20 to line 20.

Line 7 is connectable through PIP 7-14 to line 14, and through PIP 7-19to line 19, and PIP 7-20 to line 20.

Line 8 is connectable through PIP 8-13 to line 13, PIP 8-18 to line 18,and PIP 8-19 to line 19.

Line 9 is connectable through PIP 9-12 to line 12, PIP 9-17 to line 17,and PIP 9-18 to line 18.

Line 10 is connectable through PIP 10-11 to line 11, PIP 10-16 to line16, and PIP 10-17 to line 17.

The other bidirectional connections not already cited include theconnection of line 20 through PIP 20-15 to line 15, the connection ofline 19 through PIP 19-14 to line 14, the connection of line 18 throughPIP 18-13 to line 13, the connection of line 17 through PIP 17-12 toline 12, and the connection of line 16 through PIP 16-11 to line 11.

FIG. 20 illustrates the repowering buffer which is used with ahorizontal segment and a vertical segment for each switching matrix.Repowering buffers are used for reshaping a signal after it has passedthrough a number of PIPs. Each repowering buffer adds delay to the netbeing routed. Thus, for short nets, the designer would want to avoidusing the repowering buffers.

The repowering buffer as shown in FIG. 20 is connected on one of thebidirectional general interconnect segments designated line X in thefigure, where X is one of lines 5-14 in a horizontal or vertical bus.Line X enters the left side of the repowering buffer at point 2000.Point 2000 is supplied as input to a first tristate buffer 2001. Theoutput of the tristate buffer 2001 is connected to point 2002 which issupplied at the output of the repowering buffer back to line X. Point2002 is also supplied at the input of a tristate buffer 2003. The outputof the tristate buffer 2003 is connected at point 2000 for supply of thesignal in the right to left direction. A third path, through passtransistor 2004, is supplied between points 2000 and 2002. The firstmemory cell M1 and a second memory cell M2 control the operation of therepowering buffer. The true output of memory cell M1 is supplied toAND-gate 2005. The complement output of memory cell M2 is supplied as asecond input to AND-gate 2005. The output of AND-gate 2005 is thetristate enable input to buffer 2003. Likewise, the inverted output ofmemory cell M1 is supplied at a first input to AND-gate 2006. The secondinput to AND-gate 2006 is the inverted output of memory cell 2002. Theoutput of AND-gate 2006 is the tristate control signal for buffer 2001.The true output of memory cell M2 is supplied to control the passtransistor 2004.

Thus, it can be seen that the repowering buffer shown in FIG. 20supplies for repowering of a signal propagating in either directionalong line X. Likewise, when line X is used for a multi-source net inwhich signals could be propagating in either direction, the passtransistor 2004 allows for bypassing of the repowering buffer.

The line location of the repowering buffer for a given switching matrixor segment box should be determined as meets the needs of a particularapplication.

The repowering buffer should be utilized for current CMOS technology forany network path passing through around four or more PIPs, and not goingthrough a CLB or IOB.

FIG. 21 illustrates the interconnection options for a switch matrixusing the PIP array as shown in FIG. 19. The figure is a graphicalrepresentation showing the possible interconnections of each of theconnections 1-20 through the switching matrix. Thus, the possibleinterconnections of connection 1 is shown in the upper left hand corner.Likewise, the possible interconnections of connection 20 are shown inthe lower right hand corner.

FIG. 22 illustrates the interconnection array for the segment box onvertical buses 1 and 9. It can be seen that the segment box is analternative switch matrix design, adapted for the peripheral buses. Eachsegment box has 20 input connections, five on each side, as illustratedin the figure. The input connections 20 and 6 are directly connected,input connections 19 and 7 are connected, inputs 18 and 8 are connected,inputs 17 and 9 are connected, and inputs 16 and 10 are connected.Inputs 1 and 15 are connectable through PIPs to the line connectinginputs 20 and 6. Inputs 2 and 14 are connectable through respective PIPsto the line connecting inputs 9 and 7. Inputs 3 and 13 are connectablethrough PIPs to the line connecting inputs 18 and 8. Inputs 4 and 12 areconnectable through PIPs to the line connecting inputs 17 and 9.Finally, inputs 5 and 11 are connectable through PIPs to the lineconnecting inputs 16 and 10.

The segment box on the horizontal buses 1 and 9 is shown in FIG. 23. Inthis implementation, inputs 1 and 15 are connected directly, inputs 2and 14 are connected directly, inputs 3 and 13 are connected directly,inputs 4 and 12 are connected directly, and inputs 5 and 11 areconnected directly. Inputs 20 and 6 are connectable through PIPs to theline connecting inputs 1 and 15, inputs 19 and 7 are connectable throughPIPs to the line connecting inputs 2 and 14. Inputs 18 and 8 areconnectable through PIPs to the line connecting inputs 3 and 13. Inputs17 and 9 are connectable through PIPs to the line connecting inputs 4and 12. Finally, inputs 16 and 10 are connectable through PIPs to theline connecting inputs 5 and 11.

FIG. 24 graphically illustrates in the style of FIG. 21, the possibleinterconnections for each input to a segment box. These possibleinterconnections apply equally to the segment boxes on the verticalbuses and to the segment boxes on the horizontal buses.

So far, the basic interconnection structure of the programmable gatearray has been described without emphasizing the connections to theconfigurable logic blocks and the input/output blocks. Accordingly, inorder to describe those connections, a detailed description of theconfigurable logic blocks and the input/output blocks follows. Then, theconnection of the input/output blocks and configurable logic blocks tothe interconnect structure is set out.

III. Configurable Logic Block

A detailed implementation of the configurable logic block is set outwith reference to FIGS. 25-44. An overview block diagram is set out inFIG. 25.

The configurable logic block 2500 shown in FIG. 25 consists of acombinational function and control generator 2501 which receives inputsfrom four sides, schematically illustrated by buses 2502-1, 2502-2,2502-3, and 2502-4. The combinational function and control generator2501 communicates with four independently configurable output ports2503-1, 2503-2, 2503-3, and 2503-4. The output ports receive signals andsupply feedback signals to and from the combinational function andcontrol generator 2501 across respective buses 2504-1, 2504-2, 2504-3,and 2504-4. Each output port supplies a plurality of output signals,schematically illustrated by the respective output buses 2505-1, 2505-2,2505-3, and 2505-4.

The block diagram of FIG. 25 illustrates at a high level the symmetry ofthe configurable logic block 2500. Input signals can be received fromall four sides of the block, likewise, output signals can be supplied toany of the four sides of the block. Furthermore, as seen below, inputsignals from the input bus 2502 can be used to generate output signalsacross bus 2505-1, 2505-2, 2505-3, or 2505-4. Similar flexibility isprovided from all of the other input buses in the configurable logicblock.

The inputs and outputs to the configurable logic block are set out inFIG. 26. Also, a notation for the inputs and outputs is provided. It canbe seen that input signals along the top side of the bus are labeled A1through D1, EM1, EN1, FM1, FN1, G1, H1, and K1. The outputs are labelledX1 and Y1. Similarly, the suffix 2 is applied to the right side of thechip, the suffix 3 is applied to the bottom of the chip, and the suffix4 is applied to the left side of the chip. On the left side of the chip,additional inputs GR and GK for global reset and global clock signalsare provided.

As shown in the legend in FIG. 26, the inputs A1 through A4 and B1through B4 are long line inputs. Inputs C1 through C4 and D1 through D4are inputs coupled to the bidirectional general interconnect segmentsfor logic signals.

The inputs EM1 through EM4, FM1 through FM4, EN1 through EN4, and FN1through FN4 are direct connect inputs. The inputs G1 through G4 and H1through H4 are inputs to the bidirectional general interconnect segmentsfor control signals.

The inputs K1 through K4 are long line inputs from bus line 15 used forclock and clock enable functions.

Outputs are supplied at terminals X1 through X4 and Y1 through Y4.Direct connect structures are connected to X1 through X4. The generalinterconnect structures are coupled to outputs Y1 through Y4.

The combinational logic block consists of a 64 bit RAM addressed througha multiplexing tree as shown in FIG. 27, 16 additional bits of RAMaddressed through a special output multiplexer as shown in FIG. 28, fourindependent output macro cells as shown in FIGS. 29-32, and multiplexingstructures used for generation of the logic inputs to the multiplexingtree and for control signals shown in FIGS. 35-44.

The basic combinational logic function is provided by the multiplexingtree shown in FIG. 27. As stated above, 64 bits of the configurationmemory 2700 is stored with program data. A first level multiplexingstructure divides the 64 bit RAM into eight 8 bit sections. Each 8 bitsection is coupled to a 8:1 multiplexer, 2701-1 through 2701-8. The 8bit multiplexers are coupled into pairs sharing three common addresssignals VA1, VB1, VC1 for multiplexers 2701-1 and 2701-2, signals VA1,VB2, VC2 for multiplexers 2701-3 and 2701-4, signals VA3, VB3, VC3 formultiplexers 2701-5 and 2701-6, and finally, signals VA4, VB4, and VC4for multiplexers 2701-7 and 2701-8.

Eight independent outputs are generated by the eight 8:1 multiplexers.The outputs FA1 through FA4 are supplied respectively from multiplexers2701-1, 2701-3, 2701-5 and 2701-7. Outputs FB1 through FB4 are suppliedrespectively from multiplexers 2701-2, 2701-4, 2701-6 and 2701-8.

The paired outputs FA1/FB1 are supplied to cross-multiplexer 2702-1.FA2/FB2 are supplied to cross-multiplexer 2702-2. FA3/FB3 are suppliedto cross-multiplexer 2702-3. FA4/FB4 are supplied to cross-multiplexer2702-4.

The cross-multiplexers 2702-1 through 2702-4 are each coupled to arespective memory cell 2703-1 through 2703-4 in the configuration memoryto receive a respective control variable VD1 through VD4.

Cross-multiplexer 2702-1 generates outputs FC1 and FD1.Cross-multiplexer 2702-2 generates output FC2 and FD2. Cross-multiplexer2702-3 generates outputs FC3 and FD3. Cross-multiplexer 2702-4 generatesoutputs FC4 and FD4.

If the memory cell 2703-1 associated with cross-multiplexer 2701-1 isequal to 0, then the input FA1 is connected to output FC1, and the inputFB1 is connected to output FD1. The control variable VD1 coupled tocross-multiplexer 2702-1 will have no effect when memory cell 2703-1 is0. Thus, a cross-multiplexer just provides a pass through path for thesignals FA1 and FB1, such that the output FC1 and FD1 are twoindependent variables of the three control signals VA1 through VC1.

When the memory cell 2703-1 is set equal to 1, then the control inputVD1 is enabled. If VD1 is 0, then the input FA1 is connected to bothoutputs VC1 and VD1. If the logic signal VD1 is equal to 1, then theinput FB1 is connected to both outputs FC1 and FD1. Thus, when thememory cell 2703-1 is true, logic signal VD1 acts as a fourth variableso that the signal on outputs FC1/FD1 is equal to a unique combinationalfunction of the four variables VA1 through VD1.

The function of the cross-multiplexers 2702-2 through 2702-4 isidentical as to that of 2702-1 with the exception that the controlsignals VD2 through VD4 are independently supplied from the inputmultiplexing structure. Also, each memory cell 2703-2 through 2703-4 isindividually configured during programming.

The output signals FC1 and FC2 are supplied as inputs to third levelmultiplexer 2704-1. Likewise, signals FC3 and FC4 are supplied to thirdlevel multiplexer 2704-2. Logic signals VE1 and VE2 control multiplexers2704-1 and 2704-2, respectively. The output FE1 of multiplexer 2704-1and FE2 of 2704-2 represent a logic function of five variables.

The signals FE1 and FE2 are supplied as input to a fourth levelmultiplexer 2705. Multiplexer 2705 is controlled by signal VF andgenerates the output F in response to six variables.

Finally, the signal F is supplied to a special output multiplexer 2706.A second input to the multiplexer 2706 is the special output signal G.Multiplexer 2706 is controlled in response to independent variable VGand generates the output signal H.

A special output signal G is generated by the special output stage shownin FIG. 28. The special output stage consists of 16 bits of RAM 2800 inthe configuration memory. The 16 bits are coupled to a 16:1 multiplexer2801. Control inputs to the 16:1 multiplexer include the signals FD1through FD4 generated by the cross-multiplexers 2702-1 through 2702-4 inFIG. 27. Because the 16 control signals VA1 through VD1, VA2 throughVD2, VA3 through VD3, and VA4 through VD4 can be independently suppliedby the input multiplexing structure from outside the CLB, the specialoutput G represents a wide gating function of 16 variables. Thus, alimited function of 16 variables is available at the G output.

The configurable logic block of the present invention uses 64 bitscascaded with 16 bits to give the ability to decode 64 states of 16input variables.

The output macro cells for the configurable logic block are shown inFIGS. 29-32. The macro cell in FIG. 29 is coupled to outputs X1 and Y1of the configurable logic block. Inputs to the macro cell include FC1,FE1, H and FD1. The inputs FC1, FE1 and H are coupled to multiplexer2900. The output DQ1 of multiplexer 2900 is supplied as a D input toregister 2901. The output Q1 of register 2901 is coupled as an input tomultiplexer 2902. Two additional inputs to multiplexer 2902 include FC1and FE1. The output of multiplexer 2902 is coupled to line 2903. Line2903 supplies the signal QF1 as feedback to the combinational logic.Likewise, it is coupled directly to an output buffer 2904 for drivingthe output signal X1 for the direct connect.

Signal 2903 is also coupled to multiplexer 2905. The second input tomultiplexer 2905 is a signal FD1. The output TY1 of multiplexer 2905 iscoupled to a tristate output buffer 2906. The output of buffer 2906 isthe Y1 signal for connection to the interconnect structure. The tristatebuffer 2906 is controlled by the control signal OE1 generated within theconfigurable logic block as described below.

The register 2901 in the macro cell further has the ability to bepreloaded during programming. This functionality is illustrated in FIG.29A where the signal DQ1 is supplied to a multiplexer 2908. The secondinput to multiplexer 2908 is program data. The multiplexer 2908 iscontrolled by the control signal PROGRAM DONE. When PROGRAM DONE isfalse, the program data is selected through to the D input of theregister 2901. Otherwise, the signal DQ1 is supplied. Likewise, theregister 2901 is clocked at the output of gate 2909. The gate 2909provides an OR function with the frame pointer and the output ofAND-gate 2910. The inputs to AND-gate 2910 include the clock signal CKgenerated within the configurable logic block and the inverse of PROGRAMDONE. Thus, during programming stage, the clock signal is disabled andthe frame pointer is used to clock register 2901 with program data.After programming is completed, the clock signal is supplied directlythrough to the register 2901. The same structure is utilized in each ofthe macro cells, although it is not explicitly shown to clarify thediagrams.

FIG. 30 shows the macro cell supplying the outputs X2 and Y2. The inputsto macro cell 2 in FIG. 30 include FC2, FE2, H, and FD2. FC2, FE2, and Hare supplied through multiplexer 3000 to generate the signal DQ2. DQ2 issupplied to register 3001. The output Q2 of register 3001 is supplied asan input to multiplexer 3002. Other inputs to multiplexer 3002 includeFC2 and FE2. The output QF2 of multiplexer 3002 is supplied on line 3003as feedback and directly to output buffer 3004 supplying the signal X2to the direct connect.

The signal on line 3003 is also supplied to multiplexer 3005. The secondinput to multiplexer 3005 is the signal FD2. The output TY2 ofmultiplexer 3005 is supplied as an input to tristate output buffer 3006,which drives the signal Y2. Tristate buffer 3006 is controlled bycontrol signal OE2.

The output macro cell of FIG. 31 drives the signals X3 and Y3. Itsinputs include the signals FC3, FE1, D1, H and FD3. The inputs FC3, FE1,and D1 are coupled through multiplexer 3100 to supply the signal DQ3.Signal DQ3 is coupled to register 3101. The output Q3 of register 3101is supplied as an input to multiplexer 3102. Two other inputs tomultiplexer 3102 include FC3 and H. The output QF3 of multiplexer 3102is supplied on line 3103 as feedback and directly to the buffer 3104which drives the signal X3. Also, the signal on line 3103 is supplied tomultiplexer 3105. The second input to multiplexer 3105 is signal FD3.The output TY3 of multiplexer 3105 is supplied to the tristate buffer3106 driving the signal Y3. The tristate buffer 3106 is controlled bythe signal OE3.

The output macro cell for the driving signals X4 and Y4 is shown in FIG.32. It is similar to the macro cell of FIG. 31. The input signalsinclude FC4, FE2, D2, H, and FD4. The signals FC4, FE2 and D2 aresupplied through multiplexer 3200 to supply the signal DQ4. Signal DQ4is supplied through register 3101 to generate the output signal Q4. Theoutput signal Q4 is supplied to multiplexer 3102. Other inputs tomultiplexer 3102 include FC4 and H. The output of multiplexer 3102 isthe signal QF4 on line 3203 which is supplied as feedback and is coupledto buffer 3204 to drive the signal X4. The signal on line 3203 is alsosupplied to multiplexer 3205. A second input to multiplexer 3205 is thesignal FD4. Multiplexer 3205 generates a signal TY4 which is coupled tothe tristate buffer 3206. Tristate buffer 3206 is controlled by thesignal OE4 and drives the output Y4 of the configurable cell.

A design goal of the macro cells is to provide symmetrical function ofeach of the macro cells. Accordingly, to provide greater symmetry, themacro cell 1 and macro cell 2 could be changed to allow for the additionof input signals D3 and D4, respectively, at the input multiplexers 2900and 3000. Further, the ability to provide the signal H in either aregistered or combinatorial function could be allowed at each of themacro cells. The same is true for the signals FE1 and FE2. However, tooptimize utilization of the die in the preferred embodiment, the macrocells shown in FIGS. 29-32 have been adopted. Complete symmetry would beattained by replacing the 3:1 muxes with 4:2 muxes in FIGS. 29-32.

Note that the macro cells of FIGS. 31 and 32 provide for utilization ofthe registers 3101 and 3201 even if they are not used for driving theoutput of the combinational logic. This is provided by allowing theinputs D1 and D2 to be directly coupled to the registers in the outputmacro cells.

Although not shown in FIGS. 29-32, each register includes a clock, clockenable and reset control. Furthermore, each of the multiplexers shown inthe figures, unless a dynamic control signal is explicitly shown, iscontrolled by memory cells in the configuration program. Thus, theconfiguration of the macro cells is set during programming of thedevice. Note that each of the macro cells receives signals from thesecond level of multiplexing, the third level of multiplexing, and theoutput signal H.

Note also that the macro cell allows the output X1 and the output Y1 tobe driven from different sources at the same time. This gives theconfigurable logic block the ability to produce up to eight outputs at atime.

The Y1 through Y4 signals are each applied to drive eight bus lines inthe interconnect through PIPs, one of which is an uncommitted long line.The outputs X1 through X4 provide a high speed signal path to adjacentand next adjacent configurable logic cells or input/output cells in thearray.

The input multiplexing for the configurable logic block for generationof the signals VA1 through VA4 is shown in FIG. 33. The structureincludes the first 4:1 multiplexer 3300 receiving the signals A1, A2,FD2, and QF2 as inputs. The output of multiplexer 3300 is supplied as aninput to 3:1 multiplexer 3301. Two additional inputs to multiplexer 3301include FM2 and FN2. The output of multiplexer 3301 is the signal DA3 online 3302. Other inputs to the multiplexing tree include the signals C1and QF1 supplied to the 2:1 multiplexer 3303. The output of the 2:1multiplexer 3303 is the signal DA1 on line 3304. The inputs C1 and QF1are also supplied to a second input multiplexer 3310 which supplies theoutput DA2 on line 3311.

Also, the input signals EM1 and EN1 are supplied to 2:1 multiplexer3305. The output E1 is supplied on line 3306. The input D1 is coupled toline 3307.

The signal VA1 is supplied at the output of 4:1 multiplexer 3308. Thefour inputs to multiplexer 3308 include the signals D1, E1, DA1, andDA3.

The signal VA2 is supplied at the output of multiplexer 3309. The inputsto multiplexer 3309 include the signals D1, E1, DA1 and DA3.

The signal VA3 is supplied at the output of multiplexer 3312. The inputsto multiplexer 3312 include D1, E1, DA2 and DA3.

Finally, the signal VA4 is supplied at the output of 4:1 multiplexer3313. The inputs to multiplexer 3313 include D1, E1, DA2 and DA3. All ofthe multiplexers shown in FIG. 33 are controlled by memory cells in theconfiguration memory.

The control signals VB1 through VB4 are generated in the multiplexingtree which is identical to the MUX tree of FIG. 33, except that theinputs are different. Thus, the connection of the multiplexing tree isnot repeated here. Rather, only the inputs are recited. The inputs tothe multiplexing tree include FN3, FM3, A3, A4, FD3, QF3, C2, QF2, EM2,EN2, and D2. Accordingly, any one of the control signals generated bythe multiplexing tree in FIG. 34 is selected from one of eleven inputs.

Similarly, FIGS. 35 and 36 show respectively the multiplexing treesgenerating the control signals VC1 through VC4, and VD1 through VD4. Theinputs to the multiplexing tree in FIG. 35 include FN4, FM4, B1, B2,FD4, QF4, C3, QF3, EM3, EN3 and D3.

The inputs to the multiplexing tree of FIG. 36 include FN1, FM1, B3, B4,FD1, QF1, C4, QF4, EM4, EN4 and D4.

It can be seen from review of FIGS. 33-36 that the control signals VA1through VA4, VB1 through VB4, VC1 through VC4, VC1 through VD4, aregenerated using an input multiplexing tree which does not requiresharing of input variables. Furthermore, each of the outputs can bederived from an independent input variable allowing for a function offrom 1 to 16 independent variables. Furthermore, the inputs are derivedfrom all four sides of the configurable logic block allowing forsymmetrical implementation of a network on the array.

FIGS. 37, 38, and 39 illustrate generation of the control signals VE1,VE2, VF and VG. In FIG. 37, the MUX tree generates the signals VE1 andVE2 in response to the control signals CT1 and CT2 and to the inputsignals C1 and C3. VE1 is generated at the output of multiplexer 3700which receives all four of the input variables CT1, CT2, C1, C3 asinputs. The signal VE2 is generated the output of 4:1 multiplexer 3701which receives CT2, CT1, C1 and C3 as inputs.

The control signals CT1 and CT2 of FIG. 37 and CT3, CT4 and CT5 aregenerated in FIGS. 40A-40E described below.

The signal VF is generated at the output of multiplexer 3800 shown inFIG. 38. Multiplexer 3800 is a 4:1 multiplexer receiving the inputs CT3,CT4, C2 and C4.

The signal VG is generated at the output of the 3:1 multiplexer 3900shown in FIG. 39, receiving the input signals CT5, V_(CC) and GROUND.

FIGS. 40A-40H illustrates generation of the internal control signals CT1through CT8, respectively. FIG. 40A illustrates generation of the signalCT1 in response to the inputs G1 and G2 through multiplexer 4001.

FIG. 40B illustrates generation of the signal CT2 through multiplexer4002 in response to inputs G3 and G4.

FIG. 40C illustrates generation of the signal CT3 through multiplexer4003 in response to inputs H1 and H2.

FIG. 40D illustrates generation of the signal CT4 through multiplexer4004 in response to inputs H3 and H4.

FIG. 40E illustrates generation of the signal CT5 by multiplexer 4005 inresponse to inputs G1 and G2.

FIG. 40F illustrates generation of the signal CT6 by multiplexer 4006 inresponse to inputs G3 and G4.

FIG. 40G illustrates generation of the signal CT7 by multiplexer 4007 inresponse to inputs H1 and H2.

FIG. 40H illustrates generation of the signal CT8 by multiplexer 4008 inresponse to inputs H3 and H4.

FIG. 41 illustrates generation of the output enable signals OE1 throughOE4 used in the output macro cells of FIGS. 29-32. Each of the signalsOE1 through OE4 is independently supplied by respective multiplexers4100, 4101, 4102 and 4103. The inputs to multiplexers 4100, 4101, 4102and 4103 include V_(CC) and the common OE control signal on line 4104.The signal on line 4104 is generated at the output of 4:1 multiplexer4105. 4:1 multiplexer 4105 is coupled to four memory cells in theconfiguration memory 4106. Multiplexer 4105 is controlled by the signalsCT5 and CT6. Thus, each output enable signal can be configured to bestatically enabled by selecting this V_(CC) as the output signal.Alternatively, it can be dynamically enabled or disabled in response tothe common OE control signal on line 4104. Further independence ofprogramming can be accomplished by providing independent dynamic signalsfor use as the output enables.

FIG. 42 illustrates generation of the clock signal CK which is used toclock the registers in the output macro cells. This signal is generatedat the output of 2:1 multiplexer 4200. The inputs to the 2:1 multiplexer4200 include a true and complement version of the signal supplied online 4201 at the output of 6:1 multiplexer 4202.

Multiplexer 4202 receives as inputs the signals K1 through K4 from busline 15 on four sides of the macro cell, the input GK from the globalclock lines, and the control signal CT7. The multiplexers in FIG. 42 areconfigured by memory cells in the configuration memory.

FIG. 43 illustrates generation of the clock enable signal which iscoupled to the registers in the output macro cells. The clock enablesignal is generated at the output of multiplexer 4300. The input tomultiplexer 4300 includes a signal on line 4301 which is supplied at theoutput of the 3:1 multiplexer 4302. The second input to multiplexer 4300is the V_(CC) signal. Thus, the clock enable signal can be permanentlyenabled by connection to V_(CC). The inputs to multiplexer 4302 includethe K1 signal, K2 signal and the control signal CT7.

FIG. 44 illustrates generation of the reset signal RST which is suppliedto the registers in the output macro cells in the configurable logicblock. The reset signal is generated at the output of OR-gate 4400. Theinputs to OR-gate 4400 include the signal on line 4401 which isgenerated at the output of multiplexer 4402. The other input to OR-gate4400 is the global reset signal GR. The two inputs to multiplexer 4402include CT8 and GROUND. Thus, the reset signal CT8 can be permanentlyinhibited by connection to GROUND. Global reset is always allowed.

Thus, the configurable logic block described above provides forsymmetrical interfaces on all four sides of the block to theinterconnect structure. Furthermore, it allows for wide gating andnarrow gating functions without suffering a speed penalty for the narrowgated functions. Furthermore, the wide gating functions do not requiresharing of input signals which complicates logic design using theconfigurable logic block.

IV. The Input/Output Block

The configurable input/output blocks in the programmable gate array ofthe present invention consist of a simple block as shown in FIG. 45 anda complex block as shown in FIG. 46. Each input/output block (IOB) iscoupled to memory cells in the configuration memory, the states of whichcontrol the configuration of the IOB. In general, an IOB allows data topass in two directions: (i) from an input/output pad to the programmablegeneral connect and specific CLBs; (ii) from the programmable generalconnect and specific CLBs to a pad.

The configuration of an IOB sets the type of conditioning the signalreceives on passing through the IOB. The pad may or may not be bonded toa physical package pin.

There are two types of IOBs in the device. A simple IOB as shown in FIG.45 with combinatorial input and output only. Also, a complex IOB asshown in FIG. 46 provides an input register/latch and an output registerin addition to combinatorial features. The complex IOB also has internallinks for giving the user input register read-back at the package pin,and direct links to adjacent complex IOBs that allow data to betransferred to the registers of an adjacent IOB.

Note that the silicon die can be put into packages having more than,less than, or the same number of package pins as there are IOB pads onthe die. If there are fewer package pins than IOB pads, then some IOBsmay not be linked to a device package pins and so become buried IOBs forinternal device use.

As suits the needs of a particular user, the number of simple IOBs andcomplex IOBs on a given implementation may vary due to die size andspeed constraints. Further, the PGA could include all simple IOBs or allcomplex IOBs, if desired.

FIG. 45 illustrates the preferred implementation of the simple IOB.

The IOB provides a configurable interconnection between the input/outputpad 4500 and the interconnect structure. The interconnect structuresupplies output signals as inputs to multiplexer 4501. The IOB suppliesinput signals I to an interconnect bus at the output on line 4503 ofbuffer 4502. Input signals DI are coupled to adjacent configurable logicblocks at the output on line 4505 of buffer 4504.

The specific inputs to multiplexer 4501 are set out below. Each IOB hasat least one input supplied from a long line on a bus which isperpendicular to the side of the chip on which the IOB is placed. Also,it is connected to the bidirectional general interconnect lines on thebus that runs parallel to the side and to an uncommitted long line onthe bus parallel to the side. The IOB also has two direct connectinputs.

The output of multiplexer 4501 is supplied to tristate buffer 4506. Thetristate buffer 4506 has a slew rate control circuit 4507 as known inthe art. The buffer 4506 is controlled by the tristate output signal TOon line 4508.

The tristate output signal TO is supplied at the output of multiplexer4509. The inputs to multiplexer 4509 are the power supply V_(CC), thetrue and complement versions of the signal OEN which is supplied as acontrol input to the IOB from the interconnect structure, and GROUND.

When enabled, the pin output signal PO is supplied across line 4510 tothe output pad 4500. Coupled to line 4510 also is a passive pull upcircuit 4511 which is configured in response to program data throughtransistor 4512. A pull up resistor 4513 is coupled from the output oftransistor 4512 to V_(CC).

Inputs from the IO pad 4500 are supplied through buffer 4514. The outputPI of buffer 4514 is supplied on line 4515 as input to output buffer4504 and to output buffer 4502. The output buffer 4502 is a tristatebuffer controlled by the tristate input signal TI on line 4516. Thetristate input signal TI on line 4516 is generated at the output ofmultiplexer 4517. The inputs to multiplexer 4517 are V_(CC), the trueand complement of the control signal IEN which is supplied as input tothe IO block, and GROUND.

The multiplexers 4501, 4509, and 4517 are each controlled by memorycells in the configuration memory.

The signal supplied as input to buffer 4514 can be derived from threesources: the package pin coupled to the IO pad, the output PO of theoutput buffer on line 4510, or the high level created by the passivepull up circuit.

The multiplexer 4517 generates the TI signal from four sources. WhenV_(CC) is selected, the buffer 4502 is permanently enabled. When GROUNDis selected, the buffer 4502 is permanently disabled and does not switchduring operation of the programmable gate array, which could causewasted current drain. When the multiplexer 4517 is configured to selectthe IEN signal in either its true or complement form, the buffer 4502 isdynamically controlled.

The multiplexer 4501 has six inputs in the preferred system. Two of theinputs come from nearby configurable logic blocks as direct connects,the remaining come from the programmable general interconnect structure.

The output enable TO on line 4508 comes from V_(CC), OEN or GROUND. WhenV_(CC) is selected, buffer 4506 is permanently enabled. When GROUND isselected, buffer 4506 is permanently disabled. When OEN is selected, ineither its true or complement forms, buffer 4506 is dynamicallycontrolled.

The passive pull up 4511 for the output link 4510 is controlled bymemory cell 4511. When enabled, it ensures that the pad or package pindoes not float when it is not used in an application.

FIG. 46 illustrates the complex IOB. The complex IOB providesconfigurable data paths from the IO pad 4600 to the interconnect acrosslines 4601 and 4602, and from the interconnect which is coupled to theinput multiplexer 4603 to the IO pad 4600. In addition, the IOB iscoupled to the previous counterclockwise adjacent complex IOB to receiveinput signals QP1 and QP2 at lines 4604 and 4605. Also, the IOB suppliesas output the signals Q1 and Q2 to the next clockwise adjacent complexIOB on lines 4606 and 4607.

The input path includes line 4608 which is connected from the IO pad4600 as input to the input buffer 4609. The input buffer drives a signalPI on line 4610. The signal PI is coupled as an input to multiplexer4611. The second input to multiplexer 4611 is the output 4612 ofmultiplexer 4613. The inputs to multiplexer 4613 include the signals QP1and QP2.

Multiplexer 4611 is controlled in response to the signal SL1 to supplythe signal D1 on line 4614. Signal D1 is supplied at the data input ofthe input register/latch 4615. The register/latch 4615 is clocked by theoutput 4616 of multiplexer 4617. Inputs to multiplexer 4617 include thecontrol signals GK, K, and CEN which are supplied as inputs to the IOB.The register/latch further includes a global reset input 4618 whichreceives the GR signal, which is an input to the IOB. Also, a clockenable input signal LH1 is supplied on line 4619 to the register/latch4615. This signal LH1 is supplied at the output of multiplexer 4620. Theinputs to multiplexer 4620 include the CEN signal and V_(CC).

The output Q1 of the register/latch 4615 is supplied on line 4621 as aninput to multiplexer 4622, as an input to multiplexer 4623, and as theQ1 output signal on line 4606, and input to the multiplexer 4640.

A second input to multiplexer 4622 is the PI signal on line 4610. Athird input to multiplexer 4622 is the output of the output register online 4624 as described below. The output of multiplexer 4622 is suppliedto line 4625. Line 4625 is coupled as input to buffer 4626 which drivesline 4602 to the direct connect, and as input to buffer 4627 which is atristate buffer driving connections to the long lines on line 4601.Buffer 4627 is controlled by the tristate input signal on line 4628. Thesignal on line 4628 is supplied at the output of the 4:1 multiplexer4629. Inputs to the 4:1 multiplexer 4629 include the V_(CC) signal, IENin its true and complement form, and GROUND.

The output path through the complex IOB is connected to receive thesignal O on line 4630 at the output of multiplexer 4603. The signal O online 4630 is supplied as the second input to multiplexer 4623. Theoutput of multiplexer 4623 is supplied as input to multiplexer 4631. Thesecond input to multiplexer 4631 is supplied at the output ofmultiplexer 4632. The inputs to multiplexer 4632 are the QP1 and QP2signals. The output of multiplexer 4631 is the D2 signal on line 4633.The D2 signal is coupled as data input to the output register 4634.

The output register 4634 is coupled to the global reset signal GR online 4635. It is clocked by the signal K2 on line 4636 which isgenerated at the output of multiplexer 4637. Inputs to multiplexer 4637include the global clock GK, the K signal, and the CEN signal. A clockenable signal LH2 is supplied on line 4638 to the register 4634. Thesource of the signal LH2 on line 4638 is the multiplexer 4639 whichreceives as input the CEN signal and V_(CC).

The output of the register 4634 is supplied to line 4607, which drivesthe output Q2, and to line 4624, which is coupled as a first input tomultiplexer 4640 and as an input to multiplexer 4622. The second inputto multiplexer 4640 is the output Q1 of register/latch 4615 on line4621. The third input to multiplexer/latch 4615 on line 4621. The thirdinput to multiplexer 4640 is the signal O on line 4630.

The output of multiplexer 4640 is the pin output signal PO on line 4641.It is supplied through the tristate output buffer 4642 to the IO pad4600. The tristate buffer includes a slew rate control circuit 4643 asknown in the art. Further, a pass transistor 4644 and resistor 4645provide a pull up path to V_(CC) at the output of buffer 4642. This pullup path is enabled in response to the passive pull up circuit 4646 whichis implemented by a configuration memory cell.

The tristate buffer 4642 is controlled by the tristate output signal TOon line 4647. The signal is generated at the output of multiplexer 4648which receives four inputs. The inputs include V_(CC), GROUND, and atrue and complement version of the signal OEN.

Control signals K, GK, and GR are supplied directly from theinterconnect structure. The control signals IEN, CEN and OEN aresupplied at the output of respective multiplexers 4650, 4651, and 4652,each of which receives two inputs from the general interconnect.

The signal on IEN gives the ability for dynamic control of the inputpath through the buffer 4627.

The signal on OEN gives the ability for dynamic control of the outputpath through the output buffer 4642.

The signal CEN can be used as a clock or as a clock enable signal.

The signals SL1 and SL2 are derived at the output of 3:1 multiplexers4653 and 4654. Two of the inputs to the multiplexers 4653 and 4654 arederived from the interconnect structure as described below and the thirdis coupled to ground. The signal SL1 allows the input register of theIOB to be loaded with data either from the pad or from an adjacentcounterclockwise complex IOB through QP1 or QP2. The signal SL2 allowsthe output register of the IOB to be loaded with data from either theoutput of MUX 4623 or from the next adjacent counterclockwise IOBthrough QP1 or QP2.

The input register/latch 4615 can be configured to operate either as alatch or a register, in response to a memory cell in the configurationmemory. When the element operates as a register, data at the input D istransferred to the output Q on the rising edge of the clock signal K1 online 4616. When the element operates as a latch, any data change at D isseen at Q while the signal K1 is high. When K1 returns to the low state,the output Q is frozen in its present state and any change on D will notaffect the condition of Q.

The slew rate control circuit 4643 allows the output to either have afast or a slow rise time subject to the state of the memory cellcontrolling that function.

Each of the multiplexers shown in FIG. 46 is controlled by a memory cellor cells in the configuration memory with the exception of multiplexers4631 and 4611. These two multiplexers are controlled by the signals SL1and SL2.

In operation, the input path receives a signal from the pad 4600 on line4608 and passes it through buffer 4609 to generate the signal PI on line4610. The signal PI is supplied as an input to the register loadmultiplexer 4611 which is controlled by the control signal SL1. Thesecond input to the multiplexer 4611 is derived from the output ofmultiplexer 4613 which allows the supplying of a signal from either theinput register or the output register of a previous counterclockwiseadjacent complex IOB. When the signal SL1 is not connected to any linesin the circuit, it defaults to the low state allowing the signal PI topass through.

The output D1 of the multiplexer 4611 is the data input to the inputstorage element 4615. Thus, the source of data at the input storageelement is either the IO pad, the output buffer 4642, the high stategenerated by the passive pull up circuit 4646, or the input or outputregister of the adjacent complex IOB. The contents of the inputregister/latch can be frozen by asserting the signal LH1. The input pathalso includes the multiplexer 4622 which drives the output buffers 4627and 4626. The inputs to the multiplexer 4622 include the signal PI fromthe line 4610, the signal Q1 at the output of the storage element 4615,and the signal Q2 at the output of the output register 4634. Thus, theinput signals to the interconnect structure can be derived from theinput register, the combinatorial signal on line PI or from the outputregister. This allows the options for a registered or combinatorialsignal derived from the IO pad. It also allows a synchronized outputsignal which can be derived by driving the signal from the inputregister output Q1 through the output register 4634 and across line 4624back to the input driving multiplexer 4622.

The Q1 output of the input register 4615 is also available as an inputto the 3:1 multiplexer 4640 driving the signal PO. This facilitates readback of an input signal as part of the user application. Further, thesignal Q1 at the output of the input register is coupled as an input tothe 2:1 multiplexer 4623 to create the synchronization path and to theoutput pin Q1 for coupling to the next adjacent clockwise complex IOB.

The operation of the output path is similar to that of the input path.The signal O on line 4630 derived from the multiplexer 4603 comes fromeither adjacent CLBs or from the programmable general interconnectstructure for routing to the pad 4600. Through the multiplexing treecomprised of 4623 and 4631, the inputs to the output register can bederived from the signal QP1 and QP2 from the adjacent counterclockwisecomplex IOB, the output of the input register Q1 on line 4621 or fromthe signal O. The signal PO which supplies the output signal to theoutput buffer 4642 can be derived wither from the output Q2 of theoutput register 4634, the output Q1 of the input register 4615, or fromline 4630 supplying the combinatorial signal O from the output ofmultiplexer 4603.

The contents of the output register can be frozen by asserting thesignal LH2 on line 4638.

The output buffer 4642 drives both the pad 4600 and the input circuitacross line 4608. Thus, the IOB can be used as a buried structure whenthe pad is not bonded to a physical package pin.

FIGS. 47 and 48 illustrate the inputs and outputs of the complex andsimple IOBs, respectively. These figures can be referred to whenreviewing the interconnect structures described in the followingsections.

In FIG. 47, the signal DI corresponds to the signal on line 4602 in FIG.46. The signal I corresponds to the signal on line 4601 in FIG. 46. Thesignal O corresponds to the output of the multiplexer 4603. The otherlabeled signals can be clearly correlated with signals supplied in FIG.46.

Likewise, in FIG. 48, the signal DI is the signal supplied on line 4505.The signal I is the signal supplied on line 4503. The signal Ocorresponds to the output of multiplexer 4501. The IEN and OEN signalsare input control signals clearly shown in FIG. 45.

FIG. 49 illustrates conceptually the operation of the links QP1, QP2, Q1and Q2 between the complex IOBs. In the programmable gate array, theIOBs are arranged around the perimeter of the device. They are coupledto allow a clockwise data flow direction such that the inputs QP1 andQP2 are coupled to the outputs Q1 and Q2 of a next adjacentcounterclockwise complex IOB. The outputs Q1 and Q2 are coupled as inputQP1 and QP2 to the next adjacent clockwise complex IOB. In this manner,the complex IOBs can be connected together in a string allowing forimplementation of shift registers or similar structures. This increasesutilization of the logic provided in the complex IOBs, which mightotherwise be unused in a given application.

V. The Connections of Interconnect Structure to CLBs and IOBs

The configurable interconnect structure provides a means of connectingthe CLBs and IOBs together. It is divided into two major categories,called the direct connect and the programmable general connect. Theprogrammable general connect includes long lines, the bidirectionalgeneral interconnects and the uncommitted long lines.

The programmed connections required between the blocks for a userapplication are referred to as nets. A net can have single or multiplesources, and single or multiple destinations. The type of interconnectresource used to construct a net is determined from availability to thesoftware routing algorithm and the propagation delay allowed for thenet. The allowed propagation delay is defined by user application.

The direct connect structure is illustrated chiefly in FIGS. 50-55.FIGS. 50 and 51 in combination show all the direct connections suppliedas inputs EM1 through EM4, EN1 through EN4, FM1 through FM4, and FN1through FN4 supplied from the outputs X1 through X4 of eight neighborCLBs. In FIG. 50, the connection of next adjacent CLBs to the inputs FM1through FM4 and FN1 through FN4 are shown. Thus, the connection X4 fromCLB of row i-2 column j is coupled to the input FN1 of the CLB of row iin column j. Output X2 of CLB of row i-2 in column j is coupled to theinput FM3. Output X1 of CLB of row i and column j+2 is coupled to theinput FN2. Output X3 of CLB of row i column j+2 is coupled to the inputFM4. The output X4 of CLB of row i+2 in column j is coupled to the inputFM1 of the center CLB. The output X2 of row i+2 and column j is coupledto the input FN3 of the center CLB. The output X3 of the CLB of row iand column j-2 is coupled to the input FN4. Output X1 of the CLB of rowi in column j-2 is coupled to the input FM2.

As shown in FIG. 51, the output X4 of the CLB in row i-1 and column j iscoupled to the input EN1 of the center CLB in row i and column j. OutputX2 of the CLB in row i-1 and column j is coupled to the input EM3 in thecenter CLB. Output X1 of the CLB in row i and column j+1 is coupled tothe input EN2 of the center CLB. The output X3 of the CLB in row icolumn j+1 is coupled to the input EM4.

The output X2 of the CLB in row i+1 and column j is coupled to the inputEN3. The output X4 of the CLB in row i+1 in column j is coupled to theinput EM1. The output X3 of the CLB in row i and column j-1 is coupledto the input EN4. The output X1 in the CLB in row i, column j-1 iscoupled to the input EM2.

Note that the structure shown in FIGS. 50 and 51 illustrate that theCLBs in the center of the array are directly coupled to eight neighborCLBs. Further, the interconnections allow for direction of data flow inany direction through the direct connect structure among CLBs.

In an alternative system having eight neighbor CLBs, the CLB at row i-1,column j+1; row i+1, column j+1; row i-1, column j-1; and row i+1 columnj-1 could be connected in place the four outer CLbs shown in FIGS. 50and 51. This would provide eight neighbors with diagonal interconnectionpaths through the device. However, it is found that the ability totraverse a row or column with a direct connect structure provides forenhanced speed in transferring signals across the device.

FIG. 52 illustrates the connection of the outputs X1 through X4 on thecenter CLB in row i column j to the eight neighbor CLBs.

The output X4 of the CLB in the center is connected to the input FM1 ofthe CLB in row i-2, column j; the input EM1 of the CLB in row i-1,column j; the input EN1 of the CLB in row i+1, column j; and the inputFN1 in the CLB of row i+2, column j.

The output X1 is coupled to the input FN2 of the CLB in row i, columnj-2; the input EN2 in the CLB in row i, column j-1; the input EM2 in theCLB in row i, column j+1, and the input FM2 in the CLB in row i, columnj+2. The output X2 is coupled to the inputs FN3 and EN3 in the CLBs inrows i-2 and i-1, column j, respectively, and to the inputs EM3 and FM3in the CLBs of rows i+1 and i+2, of column j, respectively. Finally, theoutput X3 is coupled to the inputs FM4 and EM4 of the CLBs in row icolumns j-2 and j-1, respectively, and to the inputs EN4 and FN4 in theCLBs of row i columns j+1 and j+2, respectively.

The direct connections on the peripheral CLBs which include directconnections to the IOBs are shown in FIGS. 53-55. The figures are shownwith the IOBs along the left side of the figure so that the columns ofperipheral CLBs shown are columns 1 and 2. However, the connectionsapply as well for structures in which the peripheral CLBs are on rows 1and 2 rather than columns 1 and 2, columns 7 and 8 rather than columns 1and 2, and rows 7 and 8 rather than columns 1 and 2. The connections arejust rotated where appropriate.

Furthermore, the connections of the CLBs in the corners are not shown.These CLBs can be connected up in a wide variety of configurations dueto the converging nets at those corners. The specific direct connectionsof the corner CLBs and of all the other peripheral CLBs to IOBs on thearray are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                TO           IOB DIRECT  CLB TO                                       FROM    CLB          (DI)        IOB                                          Pad #   LOCATION     TO CLB      (O)                                          ______________________________________                                         2      R1C1         EM3         X4                                                   R2C1         FM3         X4                                            3      R1C1         FN1 FM3     X1                                                   R2C1         --          X1                                            4      R1C1         EN1         X2                                                   R2C1         FN1         X2                                            5      R1C2         EM3         X4                                                   R2C2         FM3         X4                                            6      R1C2         FN1 FM3     X1                                                   R2C2         --          X1                                            7      R1C2         EN1         X2                                                   R2C2         FN1         X2                                            8      R1C3         EM3         X4                                                   R2C3         FM3         X4                                            9      R1C3         FN1 FM3     X1                                                   R2C3         --          X1                                           10      R1C3         EN1         X2                                                   R2C3         FN1         X2                                           11      R1C4         EM3         X4                                                   R2C4         FM3         X4                                           12      R1C4         FN1 FM3     X1                                                   R2C4         --          X1                                           13      R1C4         EN1         X2                                                   R2C4         FN1         X2                                           16      R1C5         EM3         X4                                                   R2C5         FM3         X4                                           17      R1C5         FN1 FM3     X1                                                   R2C5         --          X1                                           18      R1C5         EN1         X2                                                   R2C5         FN1         X2                                           19      R1C6         EM3         X4                                                   R2C6         FM3         X4                                           20      R1C6         FN1 FM3     X1                                                   R2C6         --          X1                                           21      R1C6         EN1         X2                                                   R2C6         FN1         X2                                           22      R1C7         EM3         X4                                                   R2C7         FM3         X4                                           23      R1C7         FN1 FM3     X1                                                   R2C7         --          X1                                           24      R1C7         EN1         X2                                                   R2C7         FN1         X2                                           25      R1C8         EM3         X4                                                   R2C8         FM3         X4                                           26      R1C8         FN1 FM3     X1                                                   R2C8         --          X1                                           27      R1C8         EN1         X2                                                   R2C8         FN1         X2                                           29      R1C8         EM4         X1                                                   R1C7         FM4         X1                                           30      R1C8         FN2 FM4     X2                                                   R1C7         --          X2                                           31      R1C8         EN2         X3                                                   R1C7         FN2         X3                                           32      R2C8         EM4         X1                                                   R2C7         FM4         X1                                           33      R2C8         FN2 FM4     X2                                                   R2C7         --          X2                                           34      R2C8         EN2         X3                                                   R2C7         FN2         X3                                           35      R3C8         EM4         X1                                                   R3C7         FM4         X1                                           36      R3C8         FN2 FM4     X2                                                   R3C7         --          X2                                           37      R3C8         EN2         X3                                                   R3C7         FN2         X3                                           38      R4C8         EM4         X1                                                   R4C7         FM4         X1                                           39      R4C8         FN2 FM4     X2                                                   R4C7         --          X2                                           40      R4C8         EN2         X3                                                   R4C7         FN2         X3                                           43      R5C8         EM4         X1                                                   R5C7         FM4         X1                                           44      R5C8         FN2 FM4     X2                                                   R5C7         --          X2                                           45      R5C8         EN2         X3                                                   R5C7         FN2         X3                                           46      R6C8         EM4         X1                                                   R6C7         FM4         X1                                           47      R6C8         FN2 FM4     X2                                                   R6C7         --          X2                                           48      R6C8         EN2         X3                                                   R6C7         FN2         X3                                           49      R7C8         EM4         X1                                                   R7C7         FM4         X1                                           50      R7C8         FN2 FM4     X2                                                   R7C7         --          X2                                           51      R7C8         EN2         X3                                                   R7C7         FN2         X3                                           52      R8C8         EM4         X1                                                   R8C7         FM4         X1                                           53      R8C8         FN2 FM4     X2                                                   R8C7         --          X2                                           54      R8C8         EN2         X3                                                   R8C7         FN2         X3                                           57      R8C8         EM1         X2                                                   R7C8         FM1         X2                                           58      R8C8         FM1 FN3     X3                                                   R7C8         --          X3                                           59      R8C8         EN3         X4                                                   R7C8         FN3         X4                                           60      R8C7         EM1         X2                                                   R7C7         FM1         X2                                           61      R8C7         FM1 FN3     X3                                                   R7C7         --          X3                                           62      R8C7         EN3         X4                                                   R7C7         FN3         X4                                           63      R8C6         EM1         X2                                                   R7C6         FM1         X2                                           64      R8C6         FM1 FN3     X3                                                   R7C6         --          X3                                           65      R8C6         EN3         X4                                                   R7C6         FN3         X4                                           66      R8C5         EM1         X2                                                   R7C5         FM1         X2                                           67      R8C5         FMl FN3     X3                                                   R7C5         --          X3                                           68      R8C5         EN3         X4                                                   R7C5         FN3         X4                                           71      R8C4         EM1         X2                                                   R7C4         FM1         X2                                           72      R8C4         FM1 FN3     X3                                                   R7C4         --          X3                                           73      R8C4         EN3         X4                                                   R7C4         FN3         X4                                           74      R8C3         EM1         X2                                                   R7C3         FM1         X2                                           75      R8C3         FM1 FN3     X3                                                   R7C3         --          X3                                           76      R8C3         EN3         X4                                                   R7C3         FN3         X4                                           77      R8C2         EM1         X2                                                   R7C2         FM1         X2                                           78      R8C2         FM1 FN3     X3                                                   R7C2         --          X3                                           79      R8C2         EN3         X4                                                   R7C2         FN3         X4                                           80      R8C1         EM1         X2                                                   R7C1         FM1         X2                                           81      R8C1         FM1 FN3     X3                                                   R7C1         --          X3                                           82      R8C1         EN3         X4                                                   R7C1         FN3         X4                                           85      R8C1         EM2         X3                                                   R8C2         FM2         X3                                           86      R8C1         FM2 FN4     X4                                                   R8C2         --          X4                                           87      R8C1         EN4         X1                                                   R8C2         RN4         X1                                           88      R7C1         EM2         X3                                                   R7C2         FM2         X3                                           89      R7C1         FM2 FN4     X4                                                   R7C2         --          X4                                           90      R7C1         EN4         X1                                                   R7C2         FN4         X1                                           91      R6C1         EM2         X3                                                   R6C2         FM2         X3                                           92      R6C1         FM2 FN4     X4                                                   R6C1         --          X4                                           93      R6Cl         EN4         X1                                                   R6C2         FN4         X1                                           94      R5C1         EM2         X3                                                   R5C2         FM2         X3                                           95      R5C1         FM2 FN4     X4                                                   R5C2         --          X4                                           96      R5C1         EN4         X1                                                   R5C2         FN4         X1                                           99      R4C1         EM2         X3                                                   R4C2         FM2         X3                                           100     R4C1         FM2 FN4     X4                                                   R4C2         --          X4                                           101     R4C1         EN4         X1                                                   R4C2         FN4         X1                                           102     R3C1         EM2         X3                                                   R3C2         FM2         X3                                           103     R3C1         FM2 FN4     X4                                                   R3C2         --          X4                                           104     R3C1         EN4         X1                                                   R3C2         FN4         X1                                           105     R2C1         EM2         X3                                                   R2C2         FM2         X3                                           106     R2C1         FM2 FN4     X4                                                   R2C2         --          X4                                           107     R2C1         EN4         X1                                                   R2C2         FN4         X1                                           108     R1C1         EM2         X3                                                   R1C2         FM2         X3                                           109     R1C1         FM2 FN4     X4                                                   R1C2         --          X4                                           110     R1C1         EN4         X1                                                   R1C2         FN4         X1                                           ______________________________________                                    

FIG. 53 shows the connection of the CLB in column 1 row i, for i between3 and 6. Also, the connections of the CLB in column 2 row i are shown.

Thus, the output X1 of the CLB in column 1 row i is coupled directly toan adjacent complex IOB labelled Ri1.

Note that the IOBs in the configurable gate array of the presentinvention are grouped into three blocks per row or column of the array.Thus, as shown in FIG. 53 for row i there are three IOBs Ri1, Ri2, andRi3. Ri1 and Ri3 are complex OBs while Ri2 is a simple IOB. Each has amultiplexer receiving a plurality of signals for supply as the outputsignal to the associated pin. These inputs are shown by the reference O.

The output X1 in the CLB C1Ri is coupled directly to the output in theIOB Ri1, to the input EM2 in the CLB C2Ri and to the input FM2 in theCLB C3Ri.

The output X2 of the CLB C1Ri is coupled directly to the inputs FN3 andEN3 of the CLBs in column 1 rows Ri-2 and i-1, respectively. Also, theoutput X2 is coupled directly to the inputs EM3 and FM3 in the CLBs incolumn 1 rows Ri+1 and Ri+2, respectively.

The output X3 of the CLB C1Ri is coupled directly to the terminal O inthe complex IOB Ri3 and to the EN4 and FN4 inputs of the CLBs C2Ri andC3Ri, respectively.

The output X4 of the CLB C1Ri is coupled directly to the O terminal ofthe simple IOB Ri2 and directly to the FM1 and EM1 terminals of CLBsC1Ri-2 and C1Ri-1, respectively. Also, the output X4 of the CLB C1Ri iscoupled directly to the EN1 and FN1 inputs of CLB in column 1 rows i+1and i+2, respectively.

The output X1 in the CLB C2Ri is coupled directly to the O terminal ofthe complex IOB Ri1, and to the EN2 terminal of the CLB C1Ri. Output X1is also coupled to the EM2 and FM2 inputs of CLBs C3Ri and C4Ri,respectively.

The output X2 of the CLB C2Ri is coupled directly to the inputs FN3 andEN3 of the CLBs C2Ri-2 and C2Ri-1. The output X2 of C2Ri is also coupledto the EM3 and FM3 inputs of CLBs C2Ri+1 and C2Ri+2.

The output X3 of the CLB C2Ri is coupled directly to the O terminal ofthe complex IOB Ri3, to the EM4 input of the CLB C1Ri to the EN4 inputof CLB C3Ri and to the input FN4 of CLB C4Ri.

The output terminal X4 of the CLB C2Ri is connected directly to theinputs FM1 and EM1 of CLBs C2Ri-2 and C2Ri-1. Output X4 is also coupledto the inputs EN1 and FN1 of CLBs C2Ri+1 and C2Ri+2, respectively. Inaddition, the output X4 of CLB C2Ri is connected directly to the Oterminal of the simple IOB Ri2.

The inputs EM1 through EM4 and EN1 through EN4 of the CLB C1Ri are shownin FIG. 54. The terminal EM1 is coupled to receive the output X4 of CLBC1Ri+1. The input EN1 is coupled to receive the output X4 of the CLBC1Ri-1. The input EM2 is coupled to receive an input from the complexIOB Ri3. The input EN2 is coupled to receive the output X1 of the CLBC2Ri. The input EM3 is coupled to receive the output X2 of the CLBC1Ri-1. The input EN3 is coupled to receive the output X2 of the CLBC1Ri+1. The input EM4 is coupled to receive the output X3 of the CLBC2Ri. The input EN4 is coupled to receive an input from the complex IOBRi1.

In FIG. 55, the FM1 through FM4 and FN1 through FN4 inputs of CLBs C1Riand C2Ri are shown.

The outputs X4 of CLBs C1Ri-2 and C2Ri-2 are connected respectively tothe FN1 inputs of CLBs C1Ri and C2Ri. The outputs X2 of the CLBs C1Ri-2and C2Ri-2 are connected directly to the inputs FM3 of CLBs C1Ri andC2Ri.

The outputs X1 of the CLBs C3Ri and C4Ri are connected directly to theFN2 inputs of CLBs C1Ri and C2Ri, respectively. The outputs X3 of theCLBs C3Ri and C4Ri are connected directly to the FM4 inputs of C1Ri andC2Ri.

The outputs X2 of the CLBs C1Ri+2 and C2Ri+2 are connected directly tothe FN3 inputs of CLBs C1Ri and C2Ri, respectively. The outputs X4 ofthe CLBs C1Ri+2 and C2Ri+2 are connected directly to the FM1 inputs ofCLBs C1Ri and C2Ri, respectively.

The terminal DI of the complex IOB Ri1 is coupled directly to the FN4input of CLB C2Ri. The input DI received from the simple IOB Ri2 iscoupled directly to the FN4 input and FM2 input of the CLB C1Ri.Finally, the input signal DI derived from the complex IOB Ri3 is coupleddirectly to the FM2 input of CLB C2Ri.

The programmable general connect is illustrated in FIGS. 56-70. Itprovides a means for routing nets around the device. The CLBs and IOBsare linked through this network by means of programmable interconnectionpoints PIPs. The programmable general connect is subdivided into thelong lines and the bidirectional general interconnects BGI, which arelines incorporating metal segments spanning one or two CLBs, usuallyterminating in a switching matrix or segment box as described above withreference to FIGS. 4-24.

The selection of the location of PIPs and their connection to the inputsand outputs of the configurable logic blocks and input/output blocks isa matter of design choice. The preferred implementation is shown asfollows.

FIG. 56 shows the programmable connections of the outputs Y1 through Y4to the long lines and BGI. The outputs Y1 through Y4 are also connectedto the uncommitted long lines as shown in FIG. 58. Also, the outputs arecoupled differently to the vertical bus 1 and horizontal bus 1, verticalbus 9 and horizontal bus 9 as shown in FIG. 59 as it relates to the longlines 1-4 in the respective buses.

FIG. 56 shows that the output Y1 is coupled to PIPs associated with longlines 3, 4, and 15, and BGIs 5, 9, 13, and 14 in HBUS i. The output Y2of CLB CiRi is coupled to VBUS i+1 long lines 1 and 2 and 15, and BGIs5, 7, 11, and 14. Output Y3 of CiRi is coupled to HBUS i+1 long lines 1,2, and 15, and to BGI lines 5, 8, 12, and 14. The output Y4 of CiRi iscoupled to VBUS i long lines 3, 4, and 15, and to BGI 5, 6, 10, and 14.

Also shown in FIG. 56 are the inputs to C1 through C4 and D1 through D4.These inputs are coupled as the unidirectional PIPs using four to onemultiplexers in the preferred system to save on memory. One could usebidirectional PIPs, if desired.

The input C1 is coupled to BGI 7, 9, 11, and 13 on HBUS i. Input D1 iscoupled to BGI 6, 8, 10, and 12 on HBUS i.

Input C2 is coupled to BGI of VBUS i+1 lines 6, 8, 10, and 12, whileinput D2 is coupled to VBUS i+1 BGI 7, 9, 11, and 13.

The input C3 is coupled to HBUS i+1 BGI 6, 8, 10, and 12. Input D3 iscoupled to HBUS i+1 BGI 7, 9, 11, and 13.

The input C4 is coupled to VBUS i BGI 7, 9, 11, and 13. The input D4 iscoupled to VBUS i BGI 6, 8, 10, and 12.

FIG. 57 shows the fixed inputs from the long lines and BGI to CLB CiRifrom the adjacent buses.

For HBUS i, long line 4 is coupled to input A1, long line 3 is coupledto input B1, BGI 5 is coupled to input G1, BGI 14 is coupled to inputH1, and long line 15 is coupled to input K1.

For VBUS i+1, long line 1 is coupled to input A2, long line 2 is coupledto input B2, BGI 5 is coupled to input G2, BGI 14 is coupled to inputH2, and long line 15 is coupled to input K2.

For HBUS i+1, long line 1 is coupled to input A3, long line 2 is coupledto input B3, BGI 5 is coupled to input G3, BGI 14 is coupled to inputH3, and long line 15 is coupled to input K3.

For VBUS i, long line 4 is coupled to input A4, long line 3 is coupledto input B4, BGI 5 is coupled to input G4, BGI 14 is coupled to inputH4, long line 15 is coupled to input K4, long line 16 is coupled toinput GK, and long line 17 is coupled to input GR.

The connection of the configurable logic blocks to the uncommitted longlines is shown in FIG. 58. Each CLB, such as CLB R3C4, has outputs Y1through Y4 coupled to one uncommitted long line each. The connectionswill not be recited because they are shown in FIG. 58. In FIG. 58, onlylines 18-25 of the vertical buses, and lines 16-23 of the horizontalbuses are shown, because these are the only uncommitted long lines. Inorder to provide an example for reading FIG. 58, the CLB R3C4 output Y1is coupled to uncommitted long line 21 of HBUS 3. The output Y2 of R3C4is coupled to uncommitted long line 23 of VBUS 5. The output Y3 iscoupled to uncommitted long line 21 of HBUS 4. The output Y4 is coupledto uncommitted long line 23 of VBUS 4. Note that the uncommitted longlines do not have programmable connections to inputs of CLBs. Theselection of the connections of the outputs of the uncommitted longlines has been carried out to achieve a distributed uniform pattern thatfacilitates programming of nets through the array.

FIG. 59 shows the connection of the long lines 1-4 in HBUS 1, VBUS 1,VBUS 9, and HBUS 9. The figure shows utilization of the cornerintersections of VBUS 9 with HBUS 1 and HBUS 9, and VBUS 1 with HBUS 1and HBUS 9 to allow propagation of a signal supplied to any one of thefour outer long lines all the way around the chip. This facilitatesutilization of a single signal as a control input to all IOBs asdesired.

The outputs Y1 of CLBs in row 1 are all connected to HBUS 1 long lines1, 3, and 4 with the exception of the Y1 output of R1C8 which is coupledto HBUS 1 long lines 2, 3, and 4. The outputs Y2 of CLBs in row 1 areall connected to HBUS 1 long line 2, with the exception of R1C8. The Y4output of R1C8 is coupled to HBUS 1 long line 1.

The Y2 output of all CLBs in column 8, except for R8C8, is coupled toVBUS9 long lines 1, 2, and 4. The Y3 output of all CLBs in column 8,with the exception of C8R8, is coupled to VBUS 9 long line 3. The Y1output of C8R8 is coupled to VBUS 9 long line 4. The Y2 output of CLBC8R8 is coupled to VBUS 9 long lines 1, 2, and 3.

The Y3 outputs of all CLBs in row 8, with the exception of C1R8, arecoupled to HBUS 9 long lines 1, 2, and 4. The Y4 output of CLBs in row8, with the exception of C1R8, is coupled to HBUS 9 long line 3.

The Y2 output of C1R8 is coupled to long line 4 of HBUS 9. The Y3 outputof C1R8 is coupled to long lines 1, 2, and 3 of HBUS 9. The CLBs incolumn 1, with the exception of C1R1, are connected so that Y4 isconnected to VBUS 1 long lines 1, 3, and 4, and Y1 is connected to VBUS1 long line 2. The CLB C1R1 output Y4 is connected to VBUS 1 long lines2-4 and the output Y3 is connected to VBUS 1 long line 1.

Passage of a signal on any long line about the periphery of the chip isenabled by the interconnect structure 5900 at the intersection of VBUS 9and HBUS 1, and the interconnect structure 5901 at the intersection ofVBUS 1 and HBUS 9. These structures 5900 and 5901 allow connection of asignal on any one of the four long lines around the periphery to one ofthe two outer long lines on the respective buses, and vice versa.

FIG. 60 illustrates the long line reach between IOBs and CLBs. Ineffect, a signal input from an IOB can be supplied directly as an inputto a CLB with only one PIP delay. Also, a signal output from a CLB canbe supplied as an output signal to an IOB with only one PIP delay. Forinstance, the signal Y1 generated at CLB R6C5 can be supplied along longline 4 of HBUS 6 through PIP 6000 as an input across line 6001 to thesimple IOB R6-2. In this manner, a signal generated at CLB in theinterior of the array can be quickly propagated to the outside of thechip. Note that the symbol 6003 on long line 4 for the PIP correspondsto an input to the multiplexer 4501 of FIG. 45.

Likewise, an input signal from the IOB R6-2 and IOB R6-1 can be coupledthrough PIPs to long line 3 which is supplied as a direct input B1 toR6C5 and to R6C4. Thus, through single PIP delay, e.g. at point 6002, aninput signal from R6-1 can be supplied directly to a CLB in the interiorof the device. Similar paths can be seen from the IOBs C4-1, C4-2, C4-3,C5-1, C5-2, and C5-3 at the top or bottom of the chip. These connectionsare similarly made for IOBs at the end of each column or row in thechip.

The four long lines 1-4 of each bus have a programmable pull up resistorat their ends (not shown). These four long lines are envisioned to beused for connectivity between the IOBs and CLBs in the center of thedevice, or long reach between CLBs. The pull up resistor can be enabledby the program data in the configuration memory such that if no signalarrives at the line, the line can be taken to a logical one state. Thisstops lines from carrying spurious signals across the whole device.

A second feature of the pull up is the ability to construct a wired-ANDby driving the line from a number of CLBs or IOBs output buffers thatare tristatable.

Each output buffer may be configured such that when passing a logiczero, the buffer asserts a low to the long line. When passing a logic 1,the buffer asserts a tristate (high impedance) to the line. If no otherbuffer is driving the line (i.e., all buffers connected are intristate--the logic 1 case for each) then the pull-up resistor forces alogic high onto the line, giving the result of the AND functionrequired.

FIGS. 61-70 show connections to the IOB structure with the interconnect.In FIG. 61, the connections of the input terminals I and the outputterminals O of the eight groups of input/output blocks along the topside of the array to horizontal bus 1 are shown. In the figure, thecircular symbols at the intersection of lines refer to bidirectional PIPconnections. The squares at the intersection indicate a connection tothe multiplexer in the IOB which generates the O signal which isdescribed above with reference to FIGS. 45 and 46. It can be seen uponreview of FIG. 61 that each IOB input terminal I is coupled to one BGIand one uncommitted long line through a PIP. Each output terminal O inthe IOBs is coupled to one uncommitted long line and one BGI at theinput multiplexer. In addition, the input terminal I of the simple IOBsin respective centers of the triplets, are all coupled to long line 15through a PIP. The distribution of the connections has been chosen toprovide for a predictable scheme that facilitates programming ofnetworks on the device. A wide variety of interconnection schemes couldbe implemented as meets the needs of a specific application.

FIG. 62 illustrates the connections to the IOBs along the bottom side tohorizontal bus 9. The pattern of connections on FIG. 62 is similar tothat of FIG. 61. The same explanation applies.

FIG. 63 shows the IOB connections along the left side of the array tovertical bus 1. Again, this connection scheme is similar to that asdescribed with reference to FIG. 61 and the explanation is not restated.

FIG. 64 shows the IOB connections along the right side or the array tovertical bus 9. Again, this interconnection scheme is similar to thatdescribed with reference to FIG. 61 and is not explained again.

FIGS. 65-68 show the connections of the IOBs along the top side of thearray to the vertical buses VBUS i and VBUS i+1, and show the inputs forthe control signals GK, GR and K. Note that the input I of IOB Ci1 iscoupled through a PIP to long line 3 of VBUS i in addition to theconnections shown in FIG. 61. The terminal O of IOB Ci1 is coupledthrough the multiplexer inside the IOB to long line 4 of VBUS i. The GKand GR input signals are coupled to the long lines 16 and 17 of VBUS i.The input K is directly coupled to long line 15 of HBUS 1.

The simple IOB Ci2 has its terminal I connected through PIPs to longlines 3 and 15 of VBUS i, and long line 1 of VBUS i+1. The terminal O onthe simple IOB Ci2 receives as inputs to its multiplexer, connections tolong line 2 of VBUS i+1 and long line 4 of VBUS i.

The complex IOB Ci3 has its input terminal I coupled to long line 1 ofVBUS i+1 and a multiplexer generating the signal O coupled to receivethe signal on long line 2 of VBUS i+1. The control signals GK and GR inIOB Ci3 are coupled to long line 16 and 17 of VBUS i. Control input K iscoupled to long line 15 of HBUS 1.

FIG. 66 shows connections to the IOBs along the bottom side with thevertical buses VBUS i and VBUS i+1, as well as the control inputs K, GR,and GK. Note that the connections to these IOBs is similar to thatdescribed with reference to FIG. 65, except that the terminal I in thesimple IOB Ci2 is connected to long line 4 of VBUS i and long lines 2and 15 of VBUS i+1. In this manner, the long line 15 of VBUS i+1 isconnected to receive signals from the simple IOB Ci2 along the bottomside of the array while the VBUS i line 15 is coupled to receive asignal from the IOB at the top side of the array for IOBs over onecolumn of CLBs.

FIG. 67 shows connections to the IOBs along the left side of the arraywith the horizontal buses HBUS i and HBUS i+1 and with the controlsignals supplied along VBUS 1.

The complex IOB Ri1 receives an input from long line 3 of HBUS i at itsterminal O. The I terminal of Ri1 is coupled through a PIP to long line4 of HBUS i. Control signals K, GR and GK are coupled to lines 15, 17,and 16 respectively of VBUS 1. The output O of simple IOB Ri2 is coupledto receive inputs from long line 3 of HBUS i and long line 1 of HBUSi+1. The terminal I of simple IOB Ri2 is coupled through PIPs to longline 4 of HBUS i, long line 2 of HBUS i+1, and long line 15 of HBUS i+1.

The terminal O of complex IOB Ri3 is coupled to receive an input fromlong line 1 of HBUS i+1. The control signals K, GR, and GK are coupledto lines 15, 17, and 16 respectively of VBUS 1. The terminal I incomplex IOB Ri3 is coupled through a PIP to long line 2 of HBUS i+1.

FIG. 68 shows the connection of the IOBs along the right side of thearray to the horizontal buses HBUS i and HBUS i+1, and for receiving thecontrol signals from vertical bus VBUS 9. These connections are similarto those described with reference to FIG. 67 and are not restated. Theonly exception is that long line 15 of HBUS i is coupled to the terminalI of Ri2 along the right side (FIG. 68), while long line 15 of HBUS i+1is coupled to terminal I of the simple IOB along the left side (FIG.67).

FIG. 69 shows the connections of the other control inputs IEN, OEN, SL1,SL2, and CEN to the complex IOBs along the top and left side of thearray. Each of these signals is generated at the output of a multiplexeras is described with reference to FIG. 46. Thus, the convention of usinga square at the intersection of two lines indicates an input into themultiplexer rather than a bidirectional PIP.

Thus, as shown in FIG. 69, the inputs to the multiplexer generating thesignals IEN are supplied from long line 1 and BGI 9 of the adjacenthorizontal bus HBUS 1 for IOBs along the top, and of the adjacentvertical bus VBUS 1 for IOBs along the left side. Likewise, the signalOEN is supplied either from long line 1 or BGI 8. The signal SL1 issupplied either from long line 2 or BGI 7. The signal SL2 is suppliedeither from long line 3 of BGI 6. The signal CEN is supplied either fromlong line 4 or BGI 5.

FIG. 70 shows the inputs to the multiplexers for the control signals ofcomplex IOBs along the right and bottom sides of the array. Thus, thesignal IEN is supplied either from long line 4 or BGI 10 of VBUS 9 orHBUS 9. The signal OEN is supplied either from long line 4 or BGI 11.The signal SL1 is supplied either from long line 3 or BGI 12. The signalSL2 is supplied either from long line 2 or BGI 13. The signal CEN issupplied either from long line 1 or BGI 14.

VI. Conclusion

The present invention can be characterized as a new architecture for aprogrammable gate array device which comprises improved input/outputblocks, configurable logic blocks, and interconnect structures.

Overall, the architecture overcomes many of the problems of the priorart. The signal propagation is no longer constrained from left to rightby the interconnect structure or the input and output orientation of theCLBs. The interconnect structure of the present invention facilitatespropagation of signals across the device with few PIP delays. This isaccomplished using the BGIs that are two CLBs in length, use ofuncommitted long lines, and providing direct connection between eightneighbors.

Furthermore, the architecture eliminates the need for tristate buffersdistributed through the device that must be incorporated into a net.This is accomplished by moving the tristate buffers inside the IOBs andCLBs. Thus, for applications requiring multi-source nets, interconnectresources are not used up.

The architecture further provides a plurality of sources for clocks thatare unavailable in prior art systems. In particular, the clock can bedriven from any CLB in the array.

The present invention further provides greater utilization of theresources in the configurable input/output blocks. IOBs require a greatdeal of functionality in order to meet the flexible needs of a devicelike the programmable gate array. However, in the prior art, theseresources have only been used for input/output functions, wasting spaceand logic when not used. The present invention provides a variety ofpaths for utilizing resources of the input/output blocks for purposesother than input and output.

Furthermore, the IO blocks of the prior art are relatively slow becauseof the complex nature of the structures. Thus, the present inventionprovides the mixture of simple and complex input/output blocks. Becauseof the availability of the simple input/output blocks, the speed penaltyassociated with complex blocks can be avoided for certain applications.Furthermore, the input/output blocks of the present invention aredirectly connected to a greater number of adjacent configurable logicblocks than in the prior art. This prevents many applications frombecoming input/output bound and limiting the utilization of the logicavailable on the chip.

The configurable logic blocks according to the present inventioneliminate the sharing of input variables in wide gating functions,provide the ability to perform wide gating functions without speedpenalty for the narrow gating functions, and allow much greaterutilization of the combinational logic available in the CLB because ofthe input multiplexing structure. Furthermore, the CLBs are symmetricalin that they allow inputs and outputs from all four sides of the block,and are capable of receiving control signals and clock signals from allfour sides.

Furthermore, because of the flexibility in the input and outputstructure of the CLB, under-utilized CLBs do not suffer a speed penalty.

Overall, the present invention allows for implementation of aprogrammable gate array in which the symmetry of the interconnections,the ability to provide multi-source nets, the ability to propagatesignals long distances across the array without suffering speed penalty,and greater combinational logic capability are combined.

The present invention thus allows implementation of programmable gatearrays that are adaptable to a wider variety of applications than theprior art. Further, these implementations allow manufacture of aprogrammable gate array with greater functional density that can beefficiently utilized at a greater percentage capacity than available inprior art architectures for PGAs.

The foregoing description of preferred embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in this art.The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical application, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. A configurable logic array comprising:asubstrate; and a plurality of logic areas defined on the substrate, eachlogic area having a perimeter and programmable logic circuitrypositioned within the perimeter for performing logic operations thereinin accordance with user-provided configuration data; an interconnectnetwork defined on the substrate for carrying signals between the logicareas, wherein said interconnect network is configurable in response touser-supplied configuration data; wherein each logic area issymmetrically divisible into at least first through fourth logic areaportions; wherein each logic area includes four or more input terminalsdistributively and symmetrically positioned about the perimeter of thelogic area for receiving four or more input signals supplied fromoutside the perimeter and for conducting the four or more externallysupplied input signals into the logic area; wherein the programmablelogic circuitry of each logic area includes combinatorial logic means,operatively coupled to the four or more input terminals of the logicarea, for producing a plurality of combinatorial logic signals, eachcombinatorial logic signal being a function of one or more of theexternally supplied input signals; wherein each logic area furtherincludes a plurality of output macrocells, operatively coupled to thecorresponding combinatorial logic means of the logic area and positionedfor distributively outputting the combinatorial logic signals producedby the corresponding combinatorial logic means out of the logic areafrom at least two of the four or more area portions of the logic area;and wherein the interconnect network has nodes symmetrically distributedabout each logic area for supplying input signals to corresponding inputterminals of the logic area and for receiving the combinatorial logicsignals output from the output macrocells of the logic area.
 2. Aconfigurable logic array according to claim 1 wherein the plural logicareas are spaced apart from one another and interconnected by theconfigurable interconnect network.
 3. A configurable logic arrayaccording to claim 2 wherein the configurable interconnect networkincludes sets of interconnect buses symmetrically disposed about eachlogic area in correspondence with the symmetrically distributed inputterminals of each logic area, for supplying input signals to the inputterminals of the logic areas.
 4. A configurable logic array according toclaim 3 wherein each of the interconnect buses symmetrically disposedabout each logic area includes the same interconnect resources as foundin the other interconnect buses symmetrically disposed about the logicarea so that balanced signal routing capability is provided at eachlogic area portion of each logic area.
 5. A configurable logic arrayaccording to claim 1 wherein the interconnect network includes at leastfour tri-state lines running adjacent to the at least first throughfourth logic area portions of each of the logic areas;where there are atleast four output macrocells in each logic area; and wherein each of thefour macrocells in each logic area includes a tri-state buffer foroutputting the combinatorial logic signals produced by the correspondingcombinatorial logic means out of the logic area and onto a correspondingtri-state line adjacent to its corresponding logic area portion.
 6. Aconfigurable logic array comprising:a substrate; a configuration memorydefined on the substrate; a plurality of pads defined on the substrate,the pads being provided for conducting signals flowing between points onthe substrate and points off the substrate; a plurality of logic areasdefined on the substrate, each logic area having a perimeter and top,bottom, left and right portions within the perimeter, each logic areafurther having:four or more input terminals positioned about itsperimeter for distributively supplying four or more input signalsreceived from outside the perimeter into the top, bottom, left and rightportions, of the logic area; a combinatorial logic circuit, positionedwithin the perimeter and operatively coupled to the four or more inputterminals, for producing a plurality of combinatorial logic signals,each combinatorial logic signal being a combinatorial function of one ormore of the supplied input signals; and four output macrocells,operatively coupled to the logic circuit and positioned fordistributively outputting the combinatorial logic signals produced bythe logic circuit out of the logic area perimeter respectively from thetop, bottom, left and right portions of the logic area; and where saidconfigurable logic array further comprises: a configurable interconnectnetwork defined on the substrate for carrying signals between the logicareas; the interconnect network being symmetrically disposed relative tothe top, bottom, left and right portions of each logic area logic.